Since a few of those are fiction, it comes down to who is more powerful: the writer or the fiction? I would say the writer. So that leaves Matt vs Steve. Based on Steve's GM skils, I'll vote Steve.
What I love is that God Emperor > Matt Ward and nobody goes with Horus... I guess that has something to do that he died or something... ^^
But Matt can be beaten up by Steven Lumpkin in Real Life.... ^^ EDIT: who cares?! God Emperor is winning!