Forward clicky, multi-mode head twist
Found in many tactical lights. When the head is tightened, the light will output on maximum, with secondary outputs being accessible by loosening the head. Does not allow for one hand mode switching.
Examples include EagleTac P20C2 MkII, T20C2 MkII, 4Sevens Maelstrom G5 and Quark Tactical.
Forward clicky, multi-mode head twist, multi-bank
Same operating principal as above, but some lights can have their set of modes changed from tactical to general and back by special head twisting sequences. Does not allow for one hand mode switching.
Examples include ArmyTek Predator, Maelstrom G5 and Lumintop TD-15.
Forward clicky, multi-mode secondary switch
A recent trend, the activation switch is complemented by a secondary switch at the tailcap or towards the head for accessing strobe and switching modes. Easy one hand mode switching.
Examples include Fenix PD32, LD12 and Klarus XT series.
Single-stage, single-output
Dead-simple UI that you cannot mess up even during the most heated situations, because it has only single mode--bright. You can't, for the same reason, change modes.
Examples include Surefire 6P, C2, Z2, 6PX-T and G2X-T.
Two-stage, dual-output
Press the switch halfway for low output, put a deathgrip on it to access the maximum output. Out of all switching UIs, this offers the fastest time to change outputs, with one hand.
Examples include Surefire L1, LX2, A2 and Lumintop P16.
Forward clicky, magnetic controller
Found on certain lights, usually with tailcap switch and magnetic control ring towards the head. Outputs and modes can be adjusted via the ring, but the different positions of the switch and control ring may make it tricky to do so with one hand.
Examples include Jetbeam RRT-0 and Sunwayman V series.
Electronic switch, magnetic controller
Electronic tail switch with magnetic control ring surrounding the tailcap. Parasitic drain and tailcap fragility may be an issue, but its advantages include silent activation and near-instantaneous ability to switch between all modes using one hand.
Examples include Blackhawk Gladius and ThruNite Scorpion series.