For me it's Devil May Cry 3 for sure. In fact I think DMC 3 is one of the best games I've ever played. Even though 4 has more advanced fighting sys, better gfx, etc. I simply love the story and general over-the-topness of 3rd one. I don't really have any issues with DMC 4, only I miss Dante riding missiles and playing guitar. Also Dante vs Vergil is a lot more engaging than some random geezer.
I've also played the first one but don't really remember much, it was a great game, but still 3,3,3,3,3,3,3,3..
EDIT: I don't really understand the complain of repetitiveness in DMC 4, people don't realize that Dante was running the same hallways in DMC 1 and 3 too? (never played 2) Only in DMC 4 it's more obvious because of the linearity of stages and the character swap. But even so stages in 4 are way more varied than in earlier games.