I'm not going to pretend to know which is "best" - I can only offer my own opinions and experiences - but I'm going to wager that most people "in the know" would agree that Mcafee is crap and Norton is a shadow of it's former self.
Avira, Avast, and NOD32 are all names I've heard highly recommended. I wasn't that impressed with Avira, but Avast always did a good job. Haven't ever used NOD32.
AVG used to be popular but the free version is bloated and pretty ho-hum these days.
I've personally seen MSE catch and successfully clean up a lot of stuff that others failed to, but I would wager that a lot of that is simply a benefit of being new on the scene - crapware writers haven't had time to work out it's weaknesses yet. I could be wrong, only time will tell for sure.
Here's a site that gets mentioned a lot as one of top resources for comparing AV suites:
http://www.av-comparatives.org/