Pretty much knew right away that the only two real contenders would be Tipton/Downing and Murray/Smith. All the other pairs range from good to great, but those two are just miles and miles ahead of the others.
I voted Tipton/Downing just because of the fact that those two pretty much pioneered 90% of metal guitar that Tony Iommi didn't already invent. If anything, I've always seen Murray/Smith as a similar team but with more consistent songwriting on Smith's end. Those two definitely didn't improve their technique as much or write nearly as heavy material as Tipton/Downing though.
Edit: Also I think that Sami Yli-Sirnio and Mille Petrozza should totally be considered here. The best Kreator guitar team before those two only lasted for one good album (Petrozza/Blackfire on Coma of Souls). Sami's the best soloist Kreator's ever had and Kreator have been on an amazing hot streak for ten years now. As far as I'm concerned, he is the "classic" Kreator second guitarist.
Brocas Helm/Hatchet/Exmortus/Midnight Chaser 11/22
High on Fire/Kvelertak 12/12
Exodus/Nails/Hellfire (???) 12/20
Neurosis/Bl'ast!/YOB (???) 12/29
Last edited by Onioner; 12-26-2012 at 12:17 PM.