Well, 'bests' are always a difficult subject. Similar to what jgweed and quietman7 stated, part of the equation is usability and compatibility with your system. Some people don't like Comodo because it can produce a good number of popups, especially when not configured well. Personally, I used ZoneAlarm Free for a long time on several computers and didn't switch until the logon popup trying to get me to buy the paid version got really old. I also wanted to try Comodo because I had heard very good things about it. I'm glad I did because I think it's an excellent product and have used it since. It gives the best descriptions of what is going on that I've seen, can be configured a lot, but can also be used effectively without a lot of user configurations (if you don't mind the popups or else maybe disable Defense+). I could go on, but as you already use Comodo, I'm sure you have some of your own opinions about it. A good resource to go to that will give you more information as far as the levels of protection offered is this site:http://www.matousec.com/projects/firewall-challenge/
If you want a personal opinion, I think Comodo is the better of the two.