Microsoft Security Essentials is a nice compromise if you need to appear responsible to individuals and small businesses. It gets the job done, and it's only minimally intrusive. It also comes from a company that most people tend to trust.

Norton, on the other hand, is pure evil. If Microsoft bundled Security Essentials with Windows and thereby pushed all those pathetic AV vendors out of business (just like they did with web browsers), I might turn a blind eye this time and call it the lesser of two evils.