It depends on what you are looking for - technique or musicianship. Musically I feel the two are quite similar despite having different styles, where Slash plays mostly blues-based hard rock while Kirk plays thrash/speed metal. read more
Hammett I'd have to say is easily more technically gifted than Slash, hell, at one point he was regarded as the best metal guitarist in the world( if only, it weren't for that noodle haired Mustaine ). read more
well, slash is actually quite a sloppy player, not to mention not very technical, pretty much only plays the blues. kirk is slightly better, but is known in true metal circles to be quite overrated, and to have the worst vibrato. read more