I've tried cgminer but honestly lost patience after 1 hour not being able to get it to run, so I switched to GUIminer and it works now @~370 mhash/s. Quite okay I think. Next thing I need to investigate is the power consumption thing. Don't want to spend a fortune on power bills if there is no chance in mining enough coins in time to compensate that and still have something left.
You might like to try poclbm too.
I think GUIminer as it is at present uses poclbm by default.