I own all 3
Here is a quick rundown:
Zerorez -
PROS dead simple, reliable, unbreakable
CONS Bad for multimode lights, I highly recommend only using them on hi/lo or single level dropins only as the connection can make it skip modes and will drive you nuts. Also it is a momentary only and some batteries may be too long or not long enough so you will need to add magnets which can shift and short the light causing it to turn on! (100% reliable)
Mcclicky
PROS Forward clicky, crisp action and relatively cheap. can do 5amps no problem, cheap to replace if broken as reliable as any clicky switch (moderately-very reliable)
CONS Can break like all clickies, has steel spring that creates a moderate amount of resistance, can be very easy to accidentally activate without hardpress switchboot cover
Fettie
PROS This is the ferrari of switches, smooth action reverse clicky, nice stroke to the clicky action, no rez spring - Jesse is a very talented creator and his work is all cutting edge! (moderately-very reliable)
Cons needs a battery replacement every few years, can be fragile if you intend on hard-use and dropping on pavement although the newest ones are much tougher (has anyone broken one?), some people don't like forward clickies as there is no momentary on