I work as a computer tech and deal with numerous brands of AV software on a daily basis. The only one that catches just about everything is Norton AntiVirus 2006.
Ones that let all kinds of nasty felgercarb through include Avast!, AVG, and PC-Cillin.
Also, using only one software program to eliminate spyware doesn't work. At work we use no less than four when doing a cleanup - Spybot, Adaware, HouseCall, and Defender. Usually though, for a mild infection, the first two in that list will do the job just fine on their own.