We have been a WatchGuard shop for years and years. Recently we have had so many big problems with them we are looking to start migrating away from WatchGuard to another UTM vendor. We have from the small XTM 2 & 3 series for the Small Business and the upper-end 5 series for some top of data-center rack stuff. All together about 20 boxes. With WatchGuard we have really enjoyed the XTM manager and user interface. Because of the familiarity of the product interface and number of boxes we already had we stayed for about a year to long at WatchGuard.
We have considered the following:
Palo Alto Networks - We love them. Read great reviews about them. Just to expensive..
Fortinet - Leaning towards Fortinet. Good reviews, good products, everything seems in-house. I don't like how many switch ports the Fortigate products come with for some reason.
Check Point - Close second to Fortinet. Looking for a reason to put them first.
SonicWALL - Have read better reviews for Fortinet and Check Point.
Ultimately I am looking for somebody that is familiar with WatchGuard, Check Point and Fortinet and can provide qualified feedback. So for the small office all the way to protecting web servers.