If You are used coolminer on MPH then ZFastminer is a lot of better but in other pools coolminer works for me fine. Maybe You have some issue with which you have not met up til to use coolminer.
What's Your config of GPU, swap memory etc.?
With me, the coolminer works on 96 GTX1080 and have no problem.
All this works on ~2050MHz core and ~5005 MHz memory.

EDIT
Some day ago I was asking @Sp_ about it and
@Sp_ wrote that was trayng and practicly it has no difference in hashrate
But this is Sp_ and sometimes he only writes what he wants.