Caves can be a brutal environment for lights. In general you don't want to take a nice light (HDS, Surefire U2, etc) to many caves. Lights often get scuffed, scratched, caked with mud, dented, etc.
However this depends on the type of cave. I took my HDS to Mammoth Cave, Ky, but that was a stand-up walking tour.
For smaller caves where crawling is necessary, I'd take a less expensive light.
Your main focus should be a headlamp, not a hand held light. A hand held light should be supplementary, not the primary illumination source. See
http://www.flashlightreviews.com/ for headlamp reviews, also there are various headlamps manufactured for the mineing industry.
http://www.brightguy.com/results.php?Search=keyword&Keyword=G has a good selection of headlamps.
Each person should have at least three independent light sources, e.g. headlamp, plus flashlight, plus AAA or Photon-type light.