What game should i get Ratchet & Clank a crack in time or Modern Warfare 2?

I recently bought a ps3 and got a stack load of games with it, im only allowed to buy one more game this year though so im going to have to buy one of these games next year if i get the other one, i really loved the ratchet and clank series on ps2 but i never played any cod games since there both out around the same time which one should i get ratchet and clank or cod(i live in the uk)