It's a matter of opinion which antivirus is the best, but to me McAfee has always been heavy on resources, this goes the same with Norton. But I use Avast! Internet security and would recommend that, AVG, or Microsoft Security Essentials, as they have millions of users. People think that the more used an antivirus is, the less secure they are - this is NOT the case. The more antivirus users there are of a product, the more infections are reported, which means more virus Definitions are created, thus protecting your system from known viruses. However some antiviruses require a secondary defense method for malware, such as Avast! That I use Spybot Search and Destory with. I also have Windows Defender, which I have turned on anyways. However because Windows Defender is developed by microsoft as well as M.S.E., it is included with it, meaning M.S.E. protects against malware and viruses.
There are tons of antivirus and antispyware programs out there. But be cautioned. Only pick known softwares. Rogue antivirus software is a type of malware that poses as a legitimate antivirus program, but shows fake alerts and displays, from their scans, viruses that are not on your computer. They usually require you to BUY the product for $30-$100 in order to "Clean up" your system. Therefore it is unwise to trust certain softwares better than others.
Some real antivirus software are: Avast!, AVG, Norton Symantec, Microsoft Security Essentials, McAfee, Kaspersky, Bitdefender, ESET Nod, Avira, and Clam antivirus.
Some legit antispyware and antimalware products are: MalwareBytes, Spybot - Search and destroy, Windows defender (Not to be confused with the rogue, Win Defender 2011), and HijackThis.
So it's up to you what antivirus is the best, no one antivirus will ever stand out from the rest.