As a DC fan I would trade Deathstroke for Deadpool any day hahah. Marvel guys would probably be like NO DEAL! Anyway not only has Deadpool been inserted into many crossovers but he is also a total master of wall breaks! What's not to like!?
Marvel - DC mashup | Spider-man+Batman; Green Goblin+Joker; Captain America+Superman; Shazam+Thor; Mysterio+Riddler; Daredevil+Nightwing; Miss Marvel+Wonder Woman; Vulture+Scarecrow; Falcon+Steel; The Red Skull+Darkseid; Kraven the Hunter+Deadshot; Wolverine+Creeper; Arnim Zola+Brainiac; Deadpool; Deathstroke; Dr. Octopus+Mr. Freeze; Venom+Bane;
I personally think Deathstroke. If it were a match where that over-rated knockoff deadpool didn't have the stupid healing factor. Well, I think that deathstroke would be able to put a killing shot/stroke on the other two before they managed to kill him.