• Single AA alkaline that can also take NiMH rechargeables and 14500 LiIon rechargeables.
• Ability to turn off instantly, without having to cycle through different brightness modes along the way (single click from ON).
• Ability to turn on instantly to last brightness setting (single click from OFF).
• Ability to turn on instantly to highest brightness mode (push and hold from OFF)
• Cycle brightness modes (push and hold from ON to do a circular cycle through modes, release on chosen mode).
• All those blink, flash, strobe, SOS modes ... keep these oddball modes "hidden" from normal day-to-day operation (double-click and hold from ON to cycle through these).
• Battery charge indicator.
• Tail stand-able and anti-roll.
• Regulated, for constant light output to the 95% exhausted battery point, then low-lumen unregulated for a few minutes so you can still find a replacement battery.
• One hand operation (that means pushbutton(s), and no twist head). Loosening the head should be reserved for deactivating the light so it doesn't accidentally get turned on, not for changing modes.
• Waterproof to a few feet of submersion.
• Wide smooth beam. No central hotspot for distance.
• Only three brightness modes needed - low, medium and high. Maybe four, if you include a super-low 0.5 lumen mode. Alternative: push and hold for continuous increase in brightness until highest. Release, then push and hold again for continuous decrease in brightness until lowest. Release, push and hold again to increase brightness. Repeat as needed.
• Some kind of removable/interchangeable screw-on adapter thingy that would allow keychain/lanyard hole, magnet, pocket clip, striker (to break glass or for self defense), etc.

The closest thing to the above that I have run into, and is what I currently carry, is an "XTAR WK41". If anybody has other suggestions for something that meets most of the above criteria, I'd love to hear! I have bought, occasionally carried, but eventually abandoned the "4Sevens Quark AA" and the "Olight T15".