If you read the fact about Drogba/Villa you'd realise what I was saying.
Xavi is better than Lampard. Everyone knows that. Only bias players seem to think otherwise, and even though you're not a Chelsea fan you seem to not like Barcelona much.
Drogba is a beast when on form. No question. But when he's not on form, he's average at best. In recent weeks, he's looked poor and everyone's been able to deal with him.
David Villa is never not on form. He's always a threat, and even if he's having a bad game, he will probably score anyway. He's a constant threat, is very quick can score with both feet and his head. Can set up as well as score, and can play down the channels not just through the middle. I guess it comes with preference to your strikers. I prefer a striker to be nimble quick and a lethal finisher. You must prefer a striker to be powerful.
It's all opinion and preference, but IMO it's pretty clear Xavi and Villa > Drogba and Lampard.