1v1 could either way in my opinion but it is worth noting that if the elite were to win I doubt they would know of the self destruct bomb of the predator so that could into play and they both would be dead. Man if these two races teamed up they would make an amazing fighting force.
They're probably about as strong as each other, and the Elite have access to superior Covenant guns while Predators have much more developed close-range weapons and techniques.
...Predators seem to have more reliable cloaking tech, though, barring that annoying 'water' thing...
The Yautjas might win due to being much stronger than Elites. (Predator 2 the Yautja ran through walls. But then again, we don't know if the Elites can or not...) Maybe a draw. But there fight would be cool.
In Halo 3, the Elites are shown to be as strong as the Master Chief, i.e. they're strong enough to flip over the big mother****ing tanks, like they were little more than a Japanese school girl's dress.
Damn, just remember how much Halo 3 sucked and what a dissapointment it was, thanks.