Well even if engineers were replaced by predators, Prometheus would not be better than AVP.
Prometheus plot/story, characters and direction suck too much to be saved by such a trick.
There are just too many disapointing aspect in Prometheus.
However, at least it would have been more fun to see the predator wipe out humans as it won't do it in the Jason style but use its advanced weapons and its hunter skills to do that.
Moreover, it would probably not kill Weyland, David and Shaw as they were not armed thus not a match for him. Though it could make an exception for David. And at least we would know why it does that as it would consider armed human as mere preys.
And last but not the least it won't leave to earth to wipe out mankind but to start a giant safari.