Most large antivirus vendors don't fill me with a lot of confidence, and my theory is that at least Microsoft's own solution is going to integrate well and stay out of my face.
I'm guessing it's moved on since then, but it lost my trust. I've had to use Norton's suite before too and it had similar reliability issues.
Since using Security Essentials / Defender on Win7 and later it just works and never needs any hand-holding.
However, at work it's a different picture. We have 300 "lusers" and everyone are eager to click on the newest malware on the block with no thought of consequences.
We've tried several AV products and right now we're using BitDefender which seems to get the work done for the most parts. First time we ran it, It found our (IT dep) 10 year old Red Alert 2 .exe crack so that was quite amusing. It also has few false positives and hardly ever makes itself noticeable in resource monitor.