Two great vocalists/rhythm guitarists in groove metal: Robb Flynn of Machine head and Max Calavera of Soulfly. Who do you think is more awesome?

They are both Great and Ive seen them both live. Its almost a tie.

If we're just talking about those bands then I'd probably go with Robb Flynn. But if We're talking about when they were in Sepultura (Max) and Vio-lence (Robb) then I would go with Max Cavalera.

It really is just a matter of personal preference but I prefer the raw energy of Cavalera. In particular I like the early Sepultura records, the Nailbomb album, and more recently his work in Cavalera Conspiracy.