I've used MSE. Seems fine. But personally I like Norton Internet Security and find it completely inobtrusive running in the background. I run NIS and Windows Defender on all of my pcs (well, actually, I use Norton 360 on my wife's pc and laptops.)
I usually find Norton Internet Security 3-pc pack for around $19, and when I do, I buy several. It doesn't matter if you stock up because if you install, for example, 2010 you can immediately upgrade it to 2012.
I think a lot of people who don't like Norton are thinking of 5 years or more ago when it used to be bloated and a resource hog. It's really very good now and regularly wins "editors pick" in virus program reviews.
It runs on my htpc and I've never had it interfere with anything I was doing. Recording, playback or anything else.