Between Nemo's kill count, and Holistic Detective's armor, pitting them against each other would pretty much be be an unstoppable force against an immovable object.
I think those two are our only pre-catastrophe champions. They've been through so much, I'm not sure they're capable of dying anymore. Veritable gods, with both their skin and spirit scarred into impenetrable armor.
I decided to check their actual stats using Dwarf Companion. What I found shocked me.
You can see the skill levels are beyond anything anyone has seen before. For reference, level 15 is Legendary. Since Holistic has been beating things to death with a backpack for the last couple years (the current overseer should zoom into his inventory and designate it to be dumped), his wrestling skill is a ridiculous 77, though he has a "low" axeman skill of 37 (legendary +22). Meanwhile, Nemo has an absolutely obscene 86 swordsman skill and a very nice obsidian blade, meaning he can probably one-hit kill anything in an unmodded game.
You'll notice at the bottom the strength, ability, and toughness stats are also included. Level 5 is the max displayed in game (perfectly agile, ultra-mighty, superdwarvenly tough). However, both of our champions have much higher stats than the conventional max. 21 strength means that Holistic is more than 4x as strong as the average well-rounded legendary.
As to equipment, once you get holistic to drop his extra fucking backpack they're about equal. Neither have metal leggear, for who knows what reason, but are otherwise suited out as gods.