It's down the personal choice, I always use Norton but you'll get many people saying it's crap, the same applies to just about any other program. MS Security Essentials would be a good place to start though and if you don't like it try something else.
agree with Ömer ESET Smart Securety is the best you can get it do not interfer with games, use it for years now and never had any problem with it
what i can not say from Norton the last working pice of software they released was the norton commander back in the good ol dos days
these MS securety essentials is just a alibi scanner its only there so you can say i have a scanner but preventing
for anything you better get some real scanner like ESET