Mmm, I'm going to have to say DC on this one. Because honestly, we have omnipotence in some form on both sides. So if we disregard those shenanigans and look purely at killing power and durability with in the non-omnipotent standards... it's Doomsday over anyone at Marvel by a landslide. Well... non-sentient Doomsday, which is the current form. Not to mention, most DC characters would destroy their Marvel counterparts. Every Flash aside from Jay Garrick would destroy Quicksilver. Hulk has been fought to the point of reverting due to physical exertion, which Superman could easily pull off. Martian Manhunter is just broken.