Eternal Sonata would make a difference (it was one of my more liked games this time around, indeed joining my big three, and I only played the 360 version) but I am still not sold on the PS3 as RPG machine concept. Now you might not miss out on much if you went PS3 but I would hold it applies in reverse as well (give or take Ni No Kuni, Persona and maybe the Atelier series or Legasista). Tales of fans may have to pick up a wii or content themselves with Vesperia if they went 360 mind you. Valkyria Chronicles was since decided to be a strategy game, though still good.
If you are talking exclusives though Magna Carta II has to be mentioned. Equally as much as I find myself not a fan I probably should at least note Fable's existence.
Now if you want an actual "X is the Y machine" then the 360, though a Japanese or region free one will be required to do it properly, is the shmup machine and even probably beats out the PC here (give or take legacy and indie stuff).
I covered much of this in a thread a few weeks back anyway
http://gbatemp.net/threads/ps3-and-360-exclusives-a-discussion.360416/
Otherwise my usual policy applies
If the games do not sell it (and the libraries are near identical) then pick
1) Whatever one you like the controller for more. PS3 is a handkiller over long sessions for me, 360 one was amazing. Others have the reverse of that. Third party and adapters may be an option, though a slightly pricey one.
2) Whatever one your friends have so you can borrow and swap games as well as do multiplayer. Multiplayer may taper off as things die down. Alternatively go the opposite and when your friends decide to sell their consoles as they become old hat then you swoop in and buy it out from under them, alternatively there you borrow/swap for a week or two and knock out the exclusives you want to play.
3) Hacking. May take a higher priority than the above, do note I would not take an early model of any console save perhaps a Wii if it had not been used (a distinct possibility with the Wii).
If you have the option for a fully hacked (as in 3.55 PS3 or JTAG/RGH 360) of acceptable newness then that possibly overrides everything else. A DVD hacked/DVD emulator 360 would do well, an otherwise hacked PS3 (save for new optical emulator) should be able to be turned into a fully hacked one anyway.
Do I need anything else than a 3.55 PS3 to hack it? No special chip or so, just a USB stick?
