vs.

This isn't a one on one, this is one entire race vs another.

Chimera solely because the Predators probably don't have nearly enough numbers to counter them.

Predators are smart, and also take pride in their kills, and are not "Evil".

Chimera, especially if the chimeran virus effects predators. But either way a vehicle supported army would crush the solo hunting predators. 

The Chimera because they have some crazy high tech technology and numbers. I mean, who else can teleport an entire planet?

Chimera, simply because of the different types of chimara out there.

Xenomorphs... why do people always forget about them? After all they ARE the ultimate killing machine

Predator's are being seriously underrated here.

Weren't the Chimera defeated by having their entire fleet blown up by one Nuclear Bomb?

You don't think a couple Predators couldn't replicate that feat?

The Predators actually do have an army.  The one man killing machines are just for FUN.

The differences in weaponry used by Predator hunters and the predator army could be compaired to the differences between the weapons used by the US army, and a duck hunter.

this and they have cloaking

Predators, definitely. 

Mostly because I have no clue about Chimeras besides resistance. ^_^