For some strange reason, Norton is only heavy on system resources on certain systems, I've spent countless hours trying to diagnose the reason and still can't figure it out. I use McAfee V8 Enterprise personally due to corporate decisions made by people who really don't have a clue, but to be fair to McAfee, we have V8 on over 600 pc's and have no problems with heavy resource usage or virus problems and some of these pc's are below 1GHz!!! We have V7 Enterprise on the rest of the pc's with little or no problems as well.
As stated above, preferences ARE one thing, but these so called facts are only tested on a few pc's, we have tested various anti-virus programs on groups of machines and have found little difference between them. We use McAfee on over 1000 pc's of various spec and have virtually no problems with it at all. Granted, this is not through choice as personally I would opt for another vendor but I nor anyone else can deny the hard cold fact that we don't have problems with McAfee.
This is the Enterprise version. Don't know if it's the same as the home version or not.
But to be honest, you won't go wrong with the various free programs stated above.