It is a matter of budget. What can you afford, how much experience you have, and what sort of sites you visit.
I would put on Kaspersky security, and Spyware Doctor 5.5 or Spy Sweeper, backed up with MBAM MalwareBytes, SuperAntiSpyware, Adaware 2008, and Windows Defender.
But it is really more of a question of what to avoid, and what experience your computer friends have. Use what your friends feel comfortable with...
Spyware software is much more important than antivirus software for most users. If you go to music sites, or exchange a lot of animated cartoon jokes and photo images, it is critical.
I would do almost anything to avoid McAfee, Norton, Symantec, and Panda because I think they are all turkeys... but of course, many, many users are very happy with them.