W@W is clearly the best. Best maps in the series. Zombie mode. CO-OP campaign. The Gore. Best MP Announcers. Best game mode - WAR. The Joy of being in a tank, or blowing one up with C4. Resnov is the best campaign character too.
MW2 definitely brought the series to a new level, but also brought some bad things with it that forced Black Ops to fix. I'd say it's ranked 3rd.
Yes. This, to date WaW was the best game overall with content. Then Id say mw2
Damn, I left out best sound too. Didn't need any stupid soup cans on my ears to know exactly which direction someone was coming from. Now every game is scamming people to buy headsets to get that quality.
Oh, and best aim assist ever too. I remember just flicking the stick in someones directions with my Carbine and it would stop dead center on them. Going back and forth between multiple enemies was a breeze.