Various Firefox addons such as AdBlock, NoScript and such have probably done more to keep malware off my PC than most of the AV software, since browsing can deliver you a payload the quickest way thanks to infected ad banners. Only "real time" I have running is MSE and it, while being one of the poorer programs, hasn't found anything in a long time trying to infect me via normal browsing.
I have MBAM and SAS on hand for scans, with TDSSkiller in case I get hit with a rootkit again. I do have Spybot installled, but their "inoculation" hosts file additions seem to be increasingly rare these days and it's a super slow scanner- SAS can do in 20 minutes what Spybot takes 4-6 hours to do because Spybot uses an older method of scanning.
I considered Hitman Pro, but is it worth it when the others seem adequate for no cost?
Unfortunately, "staying offline" doesn't matter because if you have an offline PC that you install things on, it can still get hit. Too many "legit" companies are packing various PUP packages into their installers, usually because they get paid to include it. Even Adobe tries to shoehorn in some unneeded thing with every Flash update, and gog.com is doing it too. There have been cases of retail discs shipping with malware on them too because of an infection of the gold master or something else along the manufacturing lines.