I don't understand how people have virus issues as it is - but that's another story. Keep your computer clean, don't do anything dumb and you'll be fine.
If you get viruses you are probably doing something online you shouldn't be - and then at that rate it doesn't matter what you use.
If you are clean and don't torrent or pirate and only download from known and trusted sources then on W7 Defender and MSE will work fine. That's all I run.