Best for mostPevear & Volokhonsky · 1993
Pevear and Volokhonsky's version is the popular standard — faithful to Dostoevsky's jagged, contradictory narrator. Some find it less than smooth, which arguably suits a book this deliberately uncomfortable. This is where I'd start.
Best for studentsMichael R. Katz · 2001
Michael Katz's Norton Critical Edition pays special attention to the narrator's wild swings between solemnity and vulgarity, and surrounds the text with sources and criticism. The one for study, or for readers who want the conversation around the book.