It depends on the individuals. Most Aliens are more or less the same, but Predators are every bit as diverse as humans.
Obviously the Alien has all the natural advantages- tougher skin, teeth, claws, a tail & acid blood, but I wouldn't call it a one-sided fight. We've seen Predators perform great displays of power & speed, equal or even superior to an 'average' Xeno. I'm sure a veteran Yautja could take one down in hand to hand combat without weapons.