This is my experience with AV pgms.:
AVG Free is a great little AV for free and it's quite effective, but annoying in some respects.
McAfee is effective but IMHO, for those less 'puter literate.
Trend Micro ic effective and again for the homeowner/surfer.
Norton AV is effective and yes it does consume resources but not that bad as some report.
SEP Symantec Endpoint Protection is excellent and again uses system resources but at a very effective and robust results making it worth it... depending upon the user's primary use of their PC. If you're a gamer then no... but even then you can trim and control SEP's background ops. SEP is a serious software that stops bad files dead in their tracks.
If you have plenty of RAM, and good CPU, large PF swap, etc. running SEP or Norton AV isn't much of a hindrance towards performance.