Should I get Syphon Filter 1 Or 3 (ps1)? Or both of them?

So which of this two has the best missons, story,...? I have read that SF 3 is more an expension of the previous series. is there really nothing real different from the SF 1 and 2 in syphon filter 3?

NOTE: keep in minde that I buy this titles for psp.

Already thanks for all answers (and votes)!^^

Buy only SF1 and wait until SF2 gets released before buying SF3, otherwise you'll be lost plot-wise. Gamplay-wise it's all the same more or less with an emphasis on stealth on SF2.

Buy only SF1 and wait until SF2 gets released before buying SF3, otherwise you'll be lost plot-wise. Gamplay-wise it's all the same more or less with an emphasis on stealth on SF2.

Aero5555