They are extremely bad*ss no doubts one would make Wolverine look like a cheap kung fu movie back up fighter who dies in two seconds but don't think Slade is out classed here.
Pyhsical abilities are pretty even though I think Slade is faster then a Pred is and has better reaction time.
Weapons overall I give it to the Pred Slightly. Alot of variety there. But Slade's Metagernades Sword and Energy staff make up alot of ground.
Armor no question goes to Pred especially in full body armor but Slade still has some pretty good armor to and a healing factor so he basically can keep blow for blow with the Pred.
Big thing comes down to how well they stack up hand to hand. Pred obviously has all the exprience edge. They hunt the biggest and deadliest creatures ever. Slade take on Superheros yes but he hasn't been doing it for a thousand years. Slade though has a computer like brain and I think do to his reaction time and thinking ability could outsmart a Predator in battle. He would always be one step ahead of the Pred. Basically it would be one bad*ss fight to the death and I would give it 7/10 to slade based on his faster reaction time and the Pred's lack a good healing factor.