Prevx1 is indeed a great piece of software. its based on a community database which makes it a lot stronger then most others. also, it does a pretty through job of checking and rechecking after it has cleaned up any malicous items. i give it two thumbs up
as mak said, its a personal choice. i find avast detects virus's as they are come through the wire, where as avg may or may not detect it until you run a scan.