I don't like a lot of modes on a light. My preference is for single or dual mode lights. I'd rather it turn on in whatever mode I left it in last time; as a compromise I'll accept it automatically coming on in HIGH. This is because in an emergency I want max illumination, and if it's not an emergency I have time to change the modes.

Except for keychain lights and perhaps some very limited, special applications I use CR123a batteries. I do keep a few lights that use AA or AAA, always with lithiums. Personally I have little to no use for any other kind of batteries. My collection includes one legacy light that uses 3 x C-cells but if I lost that light I would not replace it.

Max power is low down my list of priorities. Sure, an uber-bright light is sometimes useful (eg weapon use, SAR) but for the most part a couple hundred to a thousand lumens on the high end is sufficient for my purposes. A LOW setting of 5-25 lumens is about right for me.

I place a premium on reliability; everything else is secondary. It doesn't matter how bright the light or how great the ergonomics if it breaks after a three foot fall from my pack. A good, intuitive UI is my next priority, good tint follows close behind in 3rd place. 4th place is output.