It depends.
If you have budget constraint, you may like to try anti virus free software. I have been using AVG Free Anti-Virus software for years. It works really fine so far.
Updates are always available. AVG Free Anti-Virus can be downloaded from http://free.avg.com/.
Maybe one of the drawbacks of freeware is limited or no technical support available. However, for personal usage, I do think that AVG Free Anti-Virus should be more than enough.
Anyway, if you are worry about technical support to the software you use, do consider fully supported commercial products from Trend Micro, Symantec, McAfee and so on.