Need the best FPS on PS3.

[Andrespetmonkey]

For single-player: Resistance
Multiplayer: Battlefield 3 (fairly steep learning curve but when you get into it, it's incredible)

Seeing as you aren't getting Battlefield 3, then get either:
Killzone 3

Resistance FoM/2 (should both be very cheap by now)

Battlefield: Bad Company 2