If hp is the factor than snorlax en lapras are even more common.
I suggest ranking by:
-Level
-The order in wich the pokemon where placed, so if you were first you get the first spot and if you are last you get the last spot.
- no double pokemon in a gym ( only one vaporeon, one snorlax etc )
- only one type (so there can only be one water type , grass type etc )
But in my opinion the ranking by lvl or no double pokemon are the best options.