Like a surprising number of products out there (wine, for example), there is low or no correlation between price and quality when it comes to anti-virus and malware protection software. I know that many IT people choose Norton or McAfee because of their long history and the name, but they are expensive and are nowhere near the best these days. Choose these options is the modern equivalent of “nobody ever got fired for buying IBM”.
I check other sources as well, but the one I trust the most right now is AV-Test.org. They refresh their results about every 6–12 months, so be sure to check back regularly—or sign up for their newsletter.
From their current results, I am standardizing my org on AVG AntiVirus for Mac. Avast and Sophos are reasonable alternatives. Unfortunately he one I had previously selected from an earlier test—Avira—has not kept up on the Mac. If your are a non-profit, you are probably most interested in these free versions. But if you are willing to pay, BitDefender and ESET look like great options.