I've used Norton, NOD32, Avast, AVG, McAfee and Kaspersky in the past. My thoughts would be:
Dont touch Norton - it may protect well but it slows systems so much it may as well be a virus especially as it is almost impossible to remove it!
NOD32 is ok and doesn't affect system performance that much - however we got a virus while using it
AVG is good but the free version is not allowed for business users
AVAST is also great but not for business users
McAfee is ok but slows systems more than others and is annoying due to constant update requests and sales emails
Kaspersky is good, doesn't cost the earth, is reliable and doesn't slow systems too much.
I'm not an expert, I do know a little but these are only my opinions so please don't take me apart for them!
I should say that I use Avast myself...