360:
Pros - marginally improved graphics, achievements, letterboxed
Cons - 360 D-pad stinks for the game, improvements are marginal at best.
PS3/PSP:
Pros - unaltered version of PSX original (for purists), playable on the home console and portable one, with the ability to transfer save files b/w the two.
Cons - are the load times the same as the PSX disc?; no improvements that 360 has.
If portable SOTN means that much to you, wait until Dracula X Chronicles comes out. If that doesn't matter, both of them are similar enough, IMO. You can't go wrong with either, though the d-pad for the PS3 is better suited for the game.
Personally, though, I wouldn't reward Sony for being slow as molasses in putting out downloadable PSX games on the PSN. We have 12-13 games total compared to Japan who has 50-70. Theirs are all priced at 600 Yen, and SOTN sets a new pricepoint at $10, which is not the direction I want to see the PSN go. That's my crabby side-point, though. They can start charging $10 for a PSX game when it starts looking like they put some effort into the PSN store. In the meantime, they ought to be ashamed of themselves.