ok in my honest opinion, i'd say that the aliens had the upper hand the whole way untill scar regained his plasma caster, also you have to remember the pred had the added advantage of teaming with the human also, i think the aliens were on the top of things from the start - in the novel there was also more than one predalien - it 'births' from one of the fiv predators but scar destroys it with his plasma caster.
www.thorndesigns.netdarkness of acheron