Another vote for the Arc +4, HDS, Novatac, Ra clicky UI here please.
I.E. a minimum travel clicky with momentary, user programmable multi mode which includes memory so you can set the light to come on at the correct level with a bit of forethought.
Second goes to multi mode twisties - twist more for brighter is the one - IE ARC 6 ( with added bonus of momentary operation via the piston), SF L1, ORB Raw, NS, SS, Ti etc., Ra Twisty and many more.
Third goes to the cycling reverse clicky types ( Fenix, Quark etc.) I find a reverse clicky to be better than forward clicky to control multi level lights - soft tap rather than full click. Even if you don't have a momentary on them. I find lights with multi mode forward clickies frustrating to use - like Lumapower connexion and Tiable TL1 IDC for instance - nice though the lights are in other ways.
Most lamented UI has to be the Nitecore D10,EX10 (pre SP) types. Lovely interface - soft click, low travel and intuitive. What a shame they changed it and dropped their advantages over other lights so quickly. The SP mode switching are annoying in the extreme, I find. Even if they worked out that most people will only need the three levels they chose for the SP in practice, they fail to realize that they appear to be taking control away from the user. Not, psychologically, a wise move in a competitive market like this one. Also the redesigned piston seems harder to operate.