Ray was kind enough to leave it to me to actually go through 2903's dynamics one by one. He's got such a great and unique position compared to just about everybody which is why he definitely wins the Best Dynamics Award.
(We've also realized that what you asked was not which character's dynamics do we like the best, but rather which dynamics in and of themselves were our favorites, but being real, 2903 would be all over that list anyway.)
999: Having the Queen of Speed placed next to him was a blessing and a curse.
It was one thing to just be a steam engine next to a diesel train and a submarine. They were a motley assortment at that point and even if there were tenuous comparisons between the three of them, there wasn't anything really be said about any of them in relation to each other. They were simply examples of their kind.
Adding 999 to the mix though put 2903 in stark contrast to her and he came up short on everything but size (oi oi oi).
She's famous, she attended both of Chicago's World's Fairs as well as others, she broke a speed record (supposedly), and she has decades of service life. And worst of all, she knows how valuable all this makes her, not only in her own right, but in relation to the MSI's collection of outdoor exhibits. Now it's not just a steam engine, a diesel, and a submarine out on the east lawn. It's the singular Queen of Speed No. 999, the one-of-a-kind yet often referred to Pioneer Zephyr, notorious (and rare) captured Nazi U-boat U-505... and in much smaller billing underneath, some null number Santa Fe engine who barely had time to do anything, spent a decade in storage, and isn't even rare in preservation since his railway was practically giving his siblings away to anyone who would take them.
But 999 is also quite canny when it comes to yard dynamics, having been in practically every kind of yard there is over her seventy years of service. She knows the highs, she knows the lows, and where Pioneer never thought 2903 had anything to feel less than for and U-505 never thought he had any right to complain, 999 best understands where his standing puts him in the collection.
It takes a while to smooth things over between them - 999 is still a star and expects to be treated as such, no matter how common engines might feel about it - but steam solidarity wins out eventually.
Pioneer: Not since The City of Salina has Pioneer had such a complicated relationship with another engine that he yet remains oblivious to. As with Salina, Pioneer represents what 2903 feels he coulda shoulda woulda been. It's not necessarily that he dislikes being a steam engine or that he wishes he'd been built a diesel. He would just have rather been a steam engine when steam was king, rather than being built ten years after Pioneer and still being a dinosaur compared to him. He was built from the start in obsolescence and has a disadvantaged service life to show for it.
But... it's not Pioneer's fault that he was built when and as he was and 2903 knows this. While he does occasionally give Pioneer grief for his idealized world view (which 2903 sees as a result of a light workload and service life of being fawned over), he knows he can't be actively hostile; no one would side with him on it, even if they might understand. Pioneer has rarely compared himself to others and even rarer still found himself lacking, so he remains blithely unaware of how much strife comparison to him causes others. That he acts as though he's on even railing with any other engine when he's led such a charmed life can be exasperating for this reason. However Pioneer sees 2903 as a friend and has always treated him as such so it would be unbecoming to spit on his olive branches or laurels or however he puts it his fancy Roman mythology.
And truthfully, 2903 doesn't want to. It'd be impossible to maintain a grudge when the guy is talking you up just as much as he does any of his other friends, much as he's able with what little there is to say about you. Even if 2903 thinks it's an act, that Pioneer makes the effort to spin him as being just as interesting and important as the rest of the yard still reliably amounts to him being a good friend and colleague. Being a little short with Pioneer when he's on his Burlington Bullshit is fine because everyone in the yard (even Pioneer himself) enjoys that to an extent; that's just good yard banter. Taking out any feelings of inadequacy on him would not be. It'd be letting his worse nature get the better of him. It'd be undignified.
On the occasion that 2903 were so foolish to try, the U-boat looming behind Pioneer would be quick to bust him down a peg further...
U-505: Less than the fact that his own service life was hampered by the war, 2903's more particular beef with U-505 is that Pioneer was so immediately friendly with him and that an enemy unit (who should be grateful to have been spared at all, let alone put up in a museum like this) would criticize his approach to a job he didn't ask for.
2903 and U-505 actually have so much in common as to be comical. They are both wartime builds, built the same year in fact. Neither of them expected to be preserved and do not particularly prefer it to the idea of being scrapped. They are even somewhat similar in how they approach their duties as exhibits. U-505 also does not interact with visitors in the way that 999 and Pioneer do, which makes his criticism of 2903's lackluster approach to guest relations rather ironic.
He has the excuse that he's better explained by his guides than trying to do so himself, whereas 2903 just feels he has not much to say. There is - unfortunately for steam engines with unremarkable work histories - so much to say about U-505 that he merits a paid tour which not only brings in extra money but is also the museum's most popular exhibit. Additionally, it means he's experienced a lot and so any step out of line on the part of 2903 gets met with some sharp comment or observation or barb to shut him down, particularly if 2903's is cutting a little too close to Pioneer. That U-505 acts as a bit of a guard dog when the banter gets a little too cutting does little to convince 2903 that Pioneer isn't some snake charmer who immediately recognized the opportunity of having an enemy warship for an ally rather than the reality that they were the only two things in that yard for a year and Pioneer was just built to befriend.
We do have one scenario we go back and forth on depending on how devoted we want to be to the grudge match, in which 2903 and U-505 weren't immediately hostile to each other. Because U-505 was painted in a rough U.S. Navy livery until just before he was moved underground and 2903's railroad was mostly inland so he was not familiar with boats, 2903 did not initially realize that U-505 was an enemy unit. U-505 just assumed 2903 understood and shared the war machine sentiment that all of them on both sides were just doing their jobs, Pioneer didn't realize that 2903 wasn't just being friendly in the same way that he is, and 2903 knows there are pockets of German settlement in America and just assumes U-505's accent has something to do with that. It's not until 999 arrives and comments on it that 2903 finds out he's been pallin' around with an enemy unit. And he feels deeply embarrassed for having fallen for this "spy trick" and Pioneer's treachery in colluding with it, despite it actually just being a farcical misunderstanding.
For his part, U-505 finds 2903's antagonism to be a small annoyance - alles kliene fishe - but it does bother him significantly that Pioneer's friendship with him precludes him from a more solid friendship with 2903. He rather thinks 2903 would be a better friend, if only for being a locomotive too. Pioneer's made his choices though and the only thing is to do what he can to make his life easier for it. U-505 is also overestimating how much trouble this causes Pioneer; he'll step in to cut 2903 down to size if he's getting too comfortable being rude, but Pioneer's got a pretty thick shotwelded hide as is. He's been politely deflecting rudeness his whole life.
Despite all of this, there is a sense of respect on both sides of this equation, although neither of them are aware that it's mutual or would admit to it out loud. 2903 does get that U-505's role is much harder to serve and there's a large measure of indignity to it. U-505, even if he does not think 2903 has any place to be ungrateful, does also relate to the feeling of not necessarily wanting the gift and responsibility of preservation. Even if he doesn't like him as an engine, U-505 does like seeing him taking to his disposition much better once he's at the IRM. Hearing some of his new stories (eavesdropping on them, which is also ironic because 2903 always listens to U-505's stories too, even if he pretends to sleep through them), U-505 rather thinks 2903 might have made a crafty war unit if he'd been built to it.
Spitfire and Stuka: These guys didn't have much to do with 2903 until the mid-70's when Stuka was sent off site for a couple years to be refurbished. Without Stuka to keep him busy, Spitfire became a bit of a nuisance to the rest of the museum, most of whom aren't sturdy enough to play with him or won't out of principle.
2903, in perhaps a prelude to his role as Yard Dad at the IRM, took it upon himself to keep Spitfire engaged and out of other engines' hair. Despite not being a war machine, he was uniquely suited to playing with Spitfire, being built quite heartily and not particularly precious about his paint.
Stuka... actually quite likes 2903 for this, which is a unique distinction among the museum's American engines. 2903 will never know because Stuka will not deign to speak English nor does he feel it's particularly important to express the sentiment. He nonetheless appreciates 2903 helping Spitfire through his absence. Plus, he thinks it's good for Spitfire to have a friend in the museum the way that he has U-505 (lol).
Pilot: As I've said before, Pilot really puts preservation into perspective for 2903. Having had Pioneer to walk him through every step of his post-service service, Pilot has always approached the job in Pioneer's fashion with some adjustments for the different nature of the IRM compared to the MSI. While the change in venue itself also did a lot for adjusting 2903's attitude by taking a lot of the downward pressure off and giving him a distinction in their collection, watching Pilot do his best every day in gratitude for that he even gets to is a humbling experience for 2903.
It's an attitude shared by nearly every piece of equipment at the IRM actually, but Pilot also has the benefit of being analogous to Pioneer here. If Pioneer was a shiny stainless steel mirror reflecting what 2903 could have been if only the world had been different, Pilot is a mirror reflecting what he could be if he were different, if he made efforts where he didn't before.
Sante Fe 92 and Silver Mate: Another big difference in his new disposition is that at the MSI, he was one of the youngest exhibits in the collection. That everyone else was older, wiser, and more worldly than him meant that he was always at a disadvantage that way too. Upon his arrival at the IRM, however, he found that now he was older than a lot of the other stock, yet still young enough to seem aspirational. Santa Fe 92 particularly admires 2903 for being from the same railroad and for being mixed traffic like him. He also shares Pioneer's admiration for steam so he thinks 2903 being there to represent both sides of their flag's motive powers is cool.
The proofing of Pilot's offsite excursions along with 999's campaign to start visits to the IRM so she can keep up with 2903 reveals another area in which he has more experience and wisdom than just about everyone else: dealing with famous engines. Especially coping with the surprise of finding that they aren't actually that different from not-famous engines at all, much to your newly rebuilt chagrin.
727: 2903 actually doesn't interact that much with 727 practically. When he is at the MSI, 727 is often taking the opportunity of 999 being busy with him to steal away somewhere herself with U-505 (a conflict of interests since U-505 does not want to be too hidden in case Pilot wants to see him). Her taste in engines is just as baffling to 2903 as it is to 999, but he thinks if U-505 was supposed to belong to someone this whole time, then it's better that he's not running around free anymore. (He is as unclear on these war machine rules as 999 is.)
More than that though, he appreciates 727 filling the social gap that his move to the IRM has left for 999. Much like his taking up with Spitfire in the 70's, it's nice to know 999 has someone to gossip with and keep her entertained since he's not there to do it himself anymore.
