DMC3.
Almost as much atmosphere as DMC1, enemies almost as good as DMC1, but overall more fun to play with the running and fighting mechanics fixed, sped up and given variety and longevity. Plus Vergil.
I think the music of DMC3 probably takes a back seat to some of the other games, but the ambient tracks are genuinely creepy if you listen to them on their own, so they do the job. Personally I find its gameplay the best in the series, best suited to my approach. I also love the Babel design of the tower, more even than Mallet.