Deadpool wins this.
He's got a healing factor that's much better than Wolverine's.
He's immortal due to his curse by Thanos.
And well Deadpool can break the 4th Wall. He has help from that.
Really? I never knew. Still Deadpool has a better healing factor than Wolverine. So that's an advantage over Deathstroke. Deadpool's healing factor is so strong. He even regrew his own head and heart back.
Deathstroke's healing factor is nothing compared to Deadpool's. Which is why I vote for the Merc with a mouth.