If this is for your home machine which runs Windows, I would just use Microsoft Security Essentials/Windows Defender. From my experience, the other vendors like to add things you don't need, like link scanning every web site. I would go to a search engine to find something and the page would spin for 5 minutes while they tried to scan all the results. A lot of the 3rd party systems have bad reputations these days, and I don't see the corporate customers I support using them.
One of my previous employers (a long time ago in computer years) was using a commercial AV and we got hit with one of the major viruses. Had to scan our PCs every day for Months. We changed AV vendors after that, but still were bitten with another virus. For better or worse, Microsoft integrating an anti-virus with Windows has killed the 3rd party anti-virus market. They tried integrating AV a long time ago, but the other vendors got the government on them to back down. Reputation wise, Microsoft had no choice. The news reports about people getting hit with viruses and malware was looking bad for them, even though the 3rd party AV missed it.