Mike, clearly.
Although, while he was still a member, Lopez tied.
Speaking of Lopez, I feel that it's a shame his bio has been taken down from the Opeth website already. I know he's left and all, but... I dunno, I think it should still be there, what with him playing on 6 of their albums.
I mean, if Mike thinks they have another like, 8 albums left in them, then fair enough, but... I feel his contribution should be recognised by maintaining some sort of bio for him.