Not sure I'm seeing how some of those ships are UEF, to be honest... sure, they have the textures and some details from other UEF units, but the overall form just doesn't 'feel' UEF. They almost feel like they're from another fictional universe, in some cases, even, not even feeling like they belong in Supreme Commander. Sure, we have very few images for spaceships in official materials of SupCom, but what we do have doesn't look like half of these, to be honest. Reminds me of the EVE Online Create A Starship Contest, where so many submissions didn't even look appropriate for the game, let alone the faction they were claiming they were meant to be for.
The UEF T2 and T3 spaceships just feel wrong for UEF overall, even if they do have some of the details right. The T1 almost looks right, but that front or 'bow' of the ship just looks odd, like a bunch of metal barrels were strapped to the front. The factory ship having the same front just spreads the pain. I seriously hope that's just a placeholder and you have a better front/nose/bow in mind. Also not sure what the obsession with having wings, particularly forward-swept wings, on spaceships is, especially UEF ones. UEF just doesn't seem like a faction to have eccentric design choices like massive wings on warships, or, with the T2 ship, those massive floating 'gun platform' looking side hulls attached by a wing structure to the main hull. On top of the fact they are only attached to the majority of the ship through potential weak points in the design that UEF military designers probably would not have approved, the overall shape of those 'platform' things is very rounded, which seems to fly in the face of blocky UEF design philosophy.
The T3 bothers me for a number of reasons- one of which is the size of those wing structures and the nacelle-looking weapon mounts on the ends of those wings that can't help but evoke thoughts of Star Trek ships- and nothing in Supreme Commander vanilla or Forged Alliance vanilla feels like Star Trek, to me, so right off the bat the thing doesn't even feel like it belongs in the same universe as a Mavor or Fat Boy. The weapons on the ends of wing-like structures certainly doesn't feel like a Supreme Commander, let alone UEF, design choice. I would be willing to overlook it if it looked more like how it is with the T1 ship's weapons, though. Something about how the T1's armaments are arranged is nowhere near as offensive to how I see Supreme Commander and UEF design.
Really, though, the seeming obsession with placing what look like nacelles on these ships just seems to make them that much less like they fit in the game world. It's not a matter of whether they're nice designs or not, though, let me clarify. I think if there wasn't the attempt to imply they are Supreme Commander ships, I'd appreciate them just fine. But they just feel wrong for the game.
The Cybran Orbital Fighter just disgusts me as a Cybran player. The UEF Orbital Fighter gets to look like a UEF fighter, but the Cybrans get what I can only describe as a kitbashed transport (it shares no design similarities with the Cybran fighters - the Prowler, Corsiar, and Gemini - while the UEF one certainly does with the Cyclone, Janus, and Wasp). The warships I almost thought looked fine, then I noticed that obsession with nacelles rear its head again. I will admit the T3 is less noticeable for this, and I actually think I could ignore that the side engines could be cut off with a well-placed shot (I'd like to see more solid connection to the main part of the ship, there), but that T1 just looks like it was cut in three parts for the hell of it. If it wasn't for that empty space between chunks of the ship only connected to the rest by a small bit of structure, I'd say that's a Cybran warship I'd be proud to command into battle.
I think the Cybran T1 and the UEF T2 are suffering from similar problems... I won't say nacelles are bad in general- In fact, if the UEF ships looked more like this:
... It wouldn't feel so bad, because that ship actually meshes fairly well with the UEF's design philosophy, even if it's from a different fictional world, and even if it does use some form of nacelles for the engines... they're just much smaller nacelles that don't account for a third of the ship.
Another example of what I would consider more UEF than the T2 and T3 UEF spaceships shown here, despite them not even being intended as UEF ships, might be these ships pictured here:
They appear to be from a Freespace project, which manages to coincidentally design ships I wouldn't find out of place among the UEF's armadas. To be honest, I could probably look at the majority of Homeworld ships, as well, and feel they match UEF better. UEF just feels like a faction that's going to just have a big, long, angular ship with not much in the way of extraneous bits poking out from the hull besides a conning tower and the weapon systems themselves. Cybrans would be more likely to have eccentric bits, if anything, and they'd all be triangular-themed or blade-like.