the lesser known coast models , being a totally consumer product, they have always used the batteries consumers already have and are used to, plus they are cheap.
the Fenix stuff, because it doesnt have a FAT head, so its not much bigger than the battery, fits in the pocket well. not a lot of extra weight of metal i dont need.
the clones of the above, which are cheap and ok, but i will have to say the fenix quality and build style has advantages.
i use MOST the coast i modded, cause its aluminum, lightweight, not much bigger than the cell that goes in it, simple cheap, and because i put a modded lens and battery and led in it.
if it wasnt modded, i would carry a fenix instead, specially one with at least 2 levels. they are lightweigh, just the right usefull beam pattern, always work, simple fit in pocket well.
the AA batteries are usually reliable, have a good lot of power in them, come in amany types and styles, and dont make a flashlight FAT, so it fits in the pocket well. the AAA stuff (even 3x AAA) just drives me up the wall because the batterys dont have enough power.