NIS has been fine in the 2 years I've been using at with my current employer (we use managed endpoint protection for business clients, which has some minor issues from time to time - especially the active network scan/security). I'm convinced CA and McAfee are the worse mainstream AV available. Everyone else (including NIS) fall into a middle of the pack 'meh' category.
I'm currently trying Ad-Aware Internet Secrity on my home machine after reading good reviews, and although it doesn't do a scheduled scan in the free version, it does seem to have a small footprint.
Avast served me well but only for the 1 year it was free, not worth paying for it. AVG completely misses stuff, but isn't a resource hog. MS security essentials has a habit of crashing and causing havoc when it does.