Nicodemus. There is a reason he has survived 2 thousand years and is as far as we know Anduriel's only host.
Sure Marcone and Namshiel are dangerous, but Marcone is barely out if his 40s and it isn't Namshiel who leads the Fallen.
Mac is bad but his power isn't really based in combat, and tbh no one is sure how much he can access..but it probably isn't much.
Cowl is the unknown. On the one hand he has proven to be far more durable than most and survived quite a few things that should have killed him. He also doesn't seem worried by death curses either. His offence of course is also quite strong, and we haven't seen the worst of it.
However, unless they know about the Noose it would be almost impossible to kill Nicodemus. Clearly he also granted a measure of super strength and speed at times from Anduriel, and Anduriel also clearly has the ability cut magic users off from their power. Without the right magic source it might be impossible to counter...I seem to remember Harry used soulfire to counter it. And we have never seen the full power of Anduriel either. Nic himself is the deadliest hand to hand combatant. But his biggest advantage is knowledge, and I suspect he would know more than the other two and be suitably prepared.
