Of the three games mentioned, UC3 is the only one I've tried and finished in 3d and all I can say that the game is a great showpiece for what can be done with s-3d when it is considered during development. Sure some scenes can use more pop-out than depth (such as opening the journal), but overall the balance is great in almost all scenes. What was very annoying to me, having a 50'' and sitting as close as possible to get in the game, was the low res and aliasing. whyme466 is wrong about the resolution during cutscenes, although it is higher than during actual gameplay and here is an article with some numbers to back this up - http://www.eurogamer.net/articles/digit ... d-3?page=2
Overall I have to say I am partly more pleased with what GOW (God of War, not Gears) Origins collection has to offer, due to image clarity and less aliasing. Although very bland (in terms of effects, objects on screen, etc.) in comparison to UC3 or Killzone 3 the internal resolution is much higher (I would go so far as to say it is actual 720p per eye).
I would of course recommend getting UC3 for all that it is, but if I have recommend a game specifically for s-3d on the ps3, than GOW Origins ( I am a little biased, since I've played all other GOW games, but I gave also played all UC games) would be it.
Of course - SOTC, UC3, Killzone 3 and Super Stardust are also a great choice.