Starcraft II Coop: The game inside the game.

[Keltest]

Yeah, this. Tychus has the heightest floor of the commanders, even if you take the worst of his mercs he is pretty decent.

I believe the heighest ceiling are kerrigan and Vorazun based on guides. Watching a good Kerrigan player makes me feel like a scrub.

Abathur has the official record for most mutations run solo on brutal (solo in this case meaning with an ally who quits at the beginning and who has no passive benefits), so by that metric, he has the highest peak power.