Slash's technically wizardry is something to behold, but Tom Morello can do things with a guitar that few others, if any, can do, so he has uniqueness going for him.
Tom Morello is the most inventive guitarist I've ever heard. RATM are arguably the only ones to have successfully done the "rap-metal" thing, and a big reason is him, he basically plays the axe like a set of turntables. And he can shred as well (check the solo in Know Your Enemy) but it doesn't really fit their music all that well.
Slash is a great player too, no question, but I'm voting Morello.



