McAfee products have a reputation for being resource hungry, as does Norton.
Some of the well-respected 'regulars' around here are great fans of Kaspersky (which, unlike the alternatives below, you have to pay for):
http://www.kaspersky.co.uk/
It's certainly been well-rated by some PC magazines, although others describe it as 'quirky' and don't rate it so well.
The majority of the remaining 'regulars', here in Technology have until recently been using AVG Free. Plenty still do, but others have reported various problems (generally with updating) associated with the latest version, resulting in large numbers of people switching to Avast! (which is also free)
If the McAfee software is a full security suite, rather than just an antivirus program, you'll need a decent firewall, such as Zone Alarm or Comodo, both of which are free. You'll also need at least one anti-spyware program. Adaware and Sybot (both free) are both popular.
Links to all of the software I've mentioned above are in my posts here:
http://www.theanswerbank.co.uk/Technology/Comp uters/Question655460.html
You should never have two anti-virus programs or two firewalls on your PC simultaneously (even if one is 'time-expired). You can't uninstall McAfee in the usual way. You need a special program to do it:
http://service.mcafee.com/FAQDocument.aspx?lc= 1033&id=TS100507
Chris