For me the best AV software ever has been, without a doubt, ESET Smart Security.
I got in touch with them back in 2006 (so a few years ago lol) as a software developer to report a Nod32 false positive on Winstep applications and they immediately invited me to become part of their beta testers group (talk about good customer service lol).
I have been running ESET AV software ever since then and I only have GREAT things to say about it, absolutely love the thing.
NEVER caused me problems (doesn't do really stupid stuff like silently blocking access to data under Public Documents just because a legit application is writing to a folder it's supposed to be able to write to, like BitDefender does with its wacko anti-ransomware pseudo-protection), very few false positives if indeed any, automatically blocks access to dubious web sites (and lets me know that is doing so and why), it's spam filter is one of the best in the industry, the Firewall has both automatic and interactive modes, and I could go on and on and on. 
