I hated the ZA interface and its lack of flexibility or configurability, however, the uncomplicated user interface suits many peoples needs. I tried several firewalls, sygate just wouldn't install on my system (failed to reboot after install), but the one I settled on was the free version of Outpost.
The free version of outpost is now very long in the tooth, but still functional. There was a terrific deal over the Christmas break upgrade to the 2.5 Pro version, one off payment and free lifetime updates.
Is it the best? that is a very subjective question and your experience level and requirements have to be the deciding factor.