I used VIPRE Antivirus Premium for a year and found it very good and Ive a good mind to use it again on my new build late this year / early next year.
Comodo Internet Security. Mainly as I like it's sandbox. Also use Malware bytes combined I feel nice and secure.
Strictly from a stability standpoint Microsoft Security essentials causes the least problems by far. Strictly in this area the ones to avoid are Symantec, Kaspersky, and Macaffee.
I dont use nor endorse any of the above personally.
Microsoft Security Essentials is available for small businesses with up to 10 PCs.And then there is something as good & comprehensive as MSE & there is NO PRICE involed regrardless of how many machines it's protecting