Both aliens & preds are extremelly strong. An average drone would probably be at least 3 or 4 times stronger than the average adult male human. A preds' strength would probably be even greater in my opinion, on average having the physical strength of 5 or more men combined. The aliens' strongest part of their body though is probably their tail, while their physical form is still very powerful, their tail most likely brandishes the majority of their strength, for reference of this, look at the scene where chopper gets impaled by grid. On average a predator would probably weigh around 350-400lbs, & grid lifted chopper like a paperweight, so xenomorphs are defenintly not lacking in the strength department.
Predators though, operate in a similar way to humans, their physical form clearly showning where the strength comes from. Predator's muscles are extremelly well toned & strengthened, probably from centuries of training, & they are able to excert an incredible amount of power. One of the better references to their strength is in the climax of AVP, where scar grabs the large chain attached to the queen, & pulls against it with enough force to drag the queen backwards. Almost like a game of tug-o-war with a 2.5 tonne monstrosity, that the queen was losing.
To conclude this, both predators & aliens are very powerful, but I firmly believe that predators have the strength advantage, & being able to haul the queen backwards probably means that it wouldn't be just drones that the preds could overpower either.