For several years, I ran free ZoneAlarm, moved to free Sygate and then back to free ZoneAlarm. I never had any issues. But I wanted better protection than just a firewall. After trying 2 behavior analyzers (ThreatFire and Mamutu), I now run Comodo's Firewall v3.5. I'm convinced that Defense + HIPS does make my PC safer.

As for the pop-ups, I switched D + over to Clean PC Mode. The number of pop-ups dropped to almost zero. Also, when I'm installing apps I know are safe, I just disable D +. Installation mode does a similar thing but as mhl notes, it sometimes doesn't see things clearly.

At this stage, I don't see switching to anything else.

(FWIW, I tried Online Armor free a few months ago. I had a few blue screen crashes, along with it forgetting my setting choices every once in a while. I quickly decided it wasn't for me...)