Fudge, that is a good question, and I will give you my viewpoint, FWIW.

Norton is good, and Norton 2009 appears to have reversed the oft-heard statement that Norton is a resource-hog. Many who shunned Norton in the past are quite happy with Norton 2009. However, the cost come renewal time are high, and often one is better off purchasing a new edition altogether, since stores like Staples, etc sell it for less than the online renewal price.
One AV I resently came across is VIPRE from Sunbelt, a Microsoft Certified Gold partner famous for their CounterSpy anti-malware. VIPRE is an AV and an anti-spyware package that is light on resources. You can download a free trial and check it out. It is only US$29.95 to purchase.
Recently, I had a Sunbelt sponsored giveaway of VIPRE on my site and the reviews and comments I received about VIPRE's performance are encouraging.
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