What works for one person, may not work that well for another. Certain products may conflict with a anti virus on one computer, but that same anti virus may not conflict on a different computer.
As long as you follow the rule of one firewall, one anti virus, and a anti spyware(some people say you need two or more) it's just a matter of what works best for the individual.
I use Avira Antivir free, ZoneAlarm free firewall and Spyware Terminator.
For scanning purposes I have SuperAntiSpyware and Malwarebytes' Antimalware.