I used to run McAfee, Spybot S&D, Malware Bites, and Firefox as a browser. Kept Firefox and all the anti virus signatures up to date. Monitored everything running in the background. Thought I was basically bomb proof. Then, over the holidays, I'm very sure that Firefox let in the worst virus / trojan I've ever seen. Tried for three months to clean it up and it had gone through my system and "broken" many of the administrative tools. I believe this was an effort by the malware to prevent detection and eradication. After months of trying, I finally had enough.
When it was time to reformat, I decided to try the kool-aid and went 100% Micro$oft. I'm currently running W7-64, IE8, Windows Firewall, and Microsoft Security Essentials.
My system has never run better. I thought I could do better, but it doesn't seem to be true. Everything now plays very nicely with each other and as I said, my system is faster than it's ever been, and this upgrade is months old.
To your question, I think the new Microsoft Security Essentials are one of if not the best suite out there today. Read the on line reviews and make up your own mind. McAfee would be my second choice.
FWIW - B.B.S.