I would run AVG and Avast. Although, honestly, it would never catch any viruses. I'm not sure what I'm doing right or what other people might be doing wrong, but I think if you're aware of where you're going on the net and what people are emailing you, you'll be fine.
For piece of mind, just set up AVG and Avast and have them auto scan. I think you can do that with one or the other. Also make sure you update your virus definitions at least weekly...daily preferably