Er. I know we all hate the arc. But Onslaught thumped Thor handily, alongside entire teams, not just 1-2 foes. The list of easy rapeages and ownings (Apocalypse, Juggernaut, Thor, oodles of teams, etc.) is > Surfer. Sorry to say.
Anything but first form (only Mags + Xavier) should beat Surfer. I'm cool if people want to take the team, but at a certain point the Surfer hype gets a little ridiculous.