In my opinion, BD headlamps are the most practical headlamps for climbers and general outdoorsmen. They are light weight, compact and plenty robust.
I bought the Gemeni (Lunar with an LED) a year ago and have absolutely loved it. I just bought a Lunar I plan to retrofit with a Luxeon Star and possibly a regulator.
The bulbs are pretty costly ($6.50 a piece), but you can get them in .4, .5 and .7 amps (the .4 and .5 come with the headlamps).
I don't know how well they would hold up to the abuses of serious caving. You may do better with a Petzl or Princeton Tech that has fewer parts if you plan on lots of abusive caving.
I have a Princeton Tech Solo, but I never use it anymore. It has no focusing abilities and has pretty low efficiency for the performance.
Don't buy the Ion unless you like paying $6 for an unusual battery.