CheckPoint has improved its ability to detect unknown malware and has integrated engines that were previously reserved for the Enterprise version (the version I use, by the way 
).
In my last test, ZoneAlarm rendered a machine totally clean the Sophos engine can be a nuisance, but as it integrates emulation systems + Cloud/ML, Sophos is not a nuisance.
As for the version, go for the most complete version, which is NextGen Extreme Security. The free version is useless and I haven't tested the other versions.
