Samuel L Jackson was solid, but he wasn't asked to do what Leo was asked to do. Leo's role was much tougher than Jackson's.
Not that I think this should be taken into account when people vote for awards, but did you know Leo legitimately cut his hand? He wasn't scripted to do it or anything, just got carried away and broke a glass, then cut his hand on a shard. Didn't break stride, just kept acting and the cameranmen just kept rolling. They used the first take of that scene in the movie, and he had to get stitches right afterward.