I say Ratchet although Jak has a better storyline and better vechiles there are more Ratchet games and more weapons plus you lvl up not just get upgrades in the Ratchet game.
Well, Ratchet and clank has the awesome weapon collection, but you have to buy the guns. Jak is cool because you don't have to buy the guns, you just unlock them, and Daxter is much cooler then Clank. I have to say that Jak has a slight advantage because you have crazy awesome free roam (2 and 3) which I really liked.