I own both games. I'l give you my rating on both of them, as they are both highly lovable games; but i would most definitly go with 'Call of Duty: Roads to Victory'
300: 8/10 addictive 3rd person fighting game, with customizable armor and weapons and challenging bosses. The story and narraration is enjoyable with splendid graphics.

Call of Duty: Roads to Victory: 9.5/10 The most intense, fun, and adicting 1st person shooting game available for the psp console yet! The graphics are at a whole new level, as I have never seen a game with better! Once you start, you can't stop.

So if you like 3rd person, go with 300, but CoD is the MUST GET game, you won't regret it

__________________