Fish by a mile. He's a better actor by a mile.
Jackson can't play a role without indulging in Jacksonisms where he lets his personality tics into every role he plays. He only has two truly outstanding performances in his career: Jules Winfield in Pulp Fiction and Stephen in Django Unchained.
Fishburne has played a ton of diverse challenging roles which require him to subvert his personality and disappear into the characters. Jackson doesn't have the subtlety to play Ike Turner, Morpheus, Jack Crawford, Furious Styles, Joshua Larabee, Othello while Fishburne could have easily played any of Jackson's character and would have done a better job.
Fishburne is a brilliant character actor while Jackson is a brilliant caricature of himself.