For the i7 ufasoft's by far.
With rpcminer-4way.exe I was getting ~7 Mh/s with my core-i5 750.
With ufasoft's I'm getting 15.5
After the difficulty jump yesterday though, I turned it off, along with my 8800GT.
For my GTX570, rpcminer-cuda.exe works best for me, about 112.5 Mh/s.
I tried phoenix and only got 105 Mh/s and it ate up one of my CPU cores as well.
What settings are you using?