Slowpoke vs. Slowking?

The difference is in the charge moves.
Slowbro has Ice beam and Water Pulse
Slowking has Fireblast and Blizzard

I think Slowbro is superior. Slowking has acess only 1 bar charg moves, and Ice Beam is a better move for defense

I agree, slowbro seems to be better ranked movesets. i sadly made the mistake of evolving a slowking and wasting a kings rock while doing so.

You mean Slowbro?
Yes. They have the same base stats and typing, but Slowbro has better moves.
For my area, defence is very important, so my Slowbro army is strictly for defence.