I would say, hands down. Spybot and Adware are the best. Both free, both upgradable.
Heres the link to spybot
http://www.safer-networking.org/
and the link to adware
http://www.lavasoftusa.com/software/adaware/
Install one at a time, upgrade them with the latest patches which are free. Then run one after the other. Your system will be spyware clean
