I have a bazillion LED flashlights. My favorite for daily carry is the FourSevens Quark 1xAA. I like if for its bullet-proof build quality and the fact that I can run it off of 14500 rechargeable LiIon, primary Lithium, NiMH, or alkaline. That flexibility in power source is great, although 99% of the time mine is running on the 14500 for maximum brightness.

Second place goes to my Olight T15 1xAA. It has all the same desireable traits as the FourSevens.

The main difference between these two lights is in the user interface. The Olight requires you to twist the head for every mode change, which requires two hands. The FourSevens requires a quick tap on the pushbutton to change modes (a one-handed operation), then you can additionally twist the head (a two-handed operation) to get two more modes that you cycle through with button taps like before (one-handed operation again). I prefer the FourSevens interface.

However, the Olight beats the FourSevens in that it remembers the last mode it was in between uses. The FourSevens has no such memory and always starts up in the default mode. The problem with this is that if you turn off the light and then immediately realize that you need it a little while longer, when you turn it back on quickly the FourSevens takes that as a mode change command. Additionally, when you use the FourSevens and then turn it off for a while and then turn it back on, you have to cycle through the modes to get back to the level you want it to be at.

Also, the FourSevens has a super low mode, much lower than the Olight. 0.2 lumens. This is useless for eyes not adapted to darkness, but is really nice for getting out of bed at night. It is a great super low level output to putz around the house in the dark when you just woke up. The battery would last forever at this low output level.

Fenix makes some nice lights too, but they don't accept the rechargeable LiIon's like the FourSevens and Olights do, so that was a non-starter for me. The rechargeable LiIon's give you higher max brightness and longer runtimes. But their output voltage is higher so lights have to be designed to work at the higher voltage as well as at the lower voltage of alkaline and NiMH batteries. The Fenix's are not designed like that.