I'm giving the vote to Samus on this one. Here's why:

#1 She is completely encapsulated in armor. Her armor is further protected by an energy field, hence her ability to absorb leftover energy from fallen enemies to heal herself. The Predator's shoulder cannon would damage her shields, but it wouldn't actually damage the suit. Because of these defenses, she has no obvious wekanesses. Predator has a lot of open area on his body.

#2 She has more versatile long-range weaponry. Power Beam doesn't work? Freeze his ass. Plasma beam not quite getting the job done? Fry his electronics with a Wave Beam. Skin too tough? Use missiles.

#3 Her X-Ray and Thermographic visors render his optical camouflage useless.

#4 The Predator's "first aid kit" takes time to use. And it doesn't "heal" him, it is simply a really neat looking wound care kit equipped with cauterization tools and pain killers.

#5 Samus has been hunting and killing things like the Predator for a long time. She's proven herself capable of taking on hordes of enemies without the need for stealth or secrecy.

The Predator would put up an entertaining fight, but he would just end up another corpse on the pile of enemies Samus has left in her wake.