So after the updates to PvP, a lot more people having been playing PvP and I've been tracking the pokemon in the battles that I've been facing.   
After a sample of 60 PvP battles, this is what I have (by % seen in matches): 
1) 36.67%: Scizor 
2) 25.0%: Azumarill, Starmie 
3) 23.33%: Blissey, Togekiss 
4) 21.67%: Gyarados 
5) 20.00%: Gengar  
6) 16.67%: Machamp 
7) 15.00%: Tyranitar 
8) 13.33%: Ferrothorn, Talonflame, Arcanine, Milotic, Skarmory, Weavile 
9) 11.67%: Sableye, Gliscor, Electivire 
10) 10%: Snorlax, Dragonite, Magnezone, Donphan   
Note: Sample is from Blue Server   
My rating is usually near the 200, but from my experience, the ratings of the players I'm against are pretty random (I've seen players from 0-450).   
I will continue updating the numbers as I play PvP.