I have asked myself that question for several years now and have actually enjoyed learning about all of the options that are available. One of my primary rules for carrying a flashlight is it can’t be too small or I’ll end up losing it. There are plenty of very powerful flashlights that cost close to $200 and can fit in your pocket, but to me that is a one heck of an expensive thing to loose. Flashlights should be small if you are carrying them all the time, but there is such a thing as too small. If it is really small you might as well put it on a keychain.
Even though I’ve been impressed with the Streamlight Nanolights and how powerful they are, I don’t like the idea of putting them on a keychain. I carry a lot of keys already and having another thing hanging in the ignition like the Streamlight Flashlights that are on a keychain makes keys kind of clunky. I find the Streamlight Polytac to be a very nice light for all around purposes because it fits my hand very well, but it’s too big to keep on a belt or in a pocket all the time. I’ve been carrying a Streamlight PT-2 or ProTac-2. There is a smaller version called the PT-2 but that is a little too small for me. The PT-2 is in the Warranty office right now because I dropped it and cracked the lense, but the flashlight still worked.