Reputation: 195Microsoft Security Essentials(Formerly BitDefender) is one I highly recommend, it is light weight, fast and has picked up/cleaned everything I have thrown at it.
AVG on the other hand is slow, has a poor track record of virus removal and has fairly high memory usage.
Decided to go with avg 2012 bought edition (friend had extra full version is why) So far so good, i have tested it for over an hour with just about anything i throw at it is instantly caught. I dont know why you said it requires a lot of memory, 50 aint much at all.