A lot of people are mentioning Alexi Laiho. You are wrong, because the post is asking who best handles vocals and guitar. Laiho is a stellar guitar player, but he's not up there on the wail/growl list, and half of Bodom's lyrics have difficulty making sense. Therefore, my choice for best guitarist/vocalist would be Mustaine, and my choice for best bassist/vocalist is a tie between Tom Araya and Les Claypool. Geddy Lee is a distant third because, though he can wail, he can't play bass as nearly well as Araya or Claypool.
Here's another suggestion, though: Hansi Kirsch from Blind Guardian.