Keep in mind that to a great extent, battery life is a function of light output. So, for example, though Brand A might have 8 hours of battery life at high, and Brand B has only 2 hours of battery life at high, given they are similar technologies, it is most likely because the light outputs are VERY different.
Actually, most likely the medium level of Brand B has similar light output and life as Brand A's high level. If you get the idea.
That is one reason I like my EOS. It has the powerful high setting, which I don't use much, but its nice to know its there if I want it. Its medium level is still plenty bright for most of my needs.
As someone else mentioned, do take note that several brands do not allow use of lithium batteries and some are not waterproof - only water resistant. My headlamps have been known to get soaked when its raining at night.
BTW, if you go the EOS route, make sure you get the newer Rebel version. It has a much nicer output.