What Kind of Camera Should I Buy?

I get asked this question a lot though I don't really think of myself as a good resource for shopping advice. That said, I can offer a few things to think about when purchasing a camera. 

Resources for Research
If you want to look at cameras side by side, DPReview has a nice interface for doing that. It is recommended that you use this and learn what the specs mean.

Another good site with great reviews is The Digital Picture.

Here are some things I universally recommend (which are nearly universal on quality cameras now): RAW image support, a decent selection of lenses or an adapter to a type of lens with a decent selection, and 10+ megapixels.

Mirrorless cameras are lighter and take up less space. This is advantageous for cavers since there's less stuff to carry around. The disadvantage is that the energy consumption. Active LCDs take a lot of energy, so you'll want to have a few spare batteries charged and laying around. Also, they do not sell battery grips for most of the mirrorless cameras that I have seen.

SLRs are heavier and larger, but their batteries last for a considerably longer time.

Get a brand that your close friends use. That way you can borrow their lenses and trade gear if you need it. I don't care for any single brand over the others.

Personally, I shoot a Canon. I use a Canon because the firmware is so terrible. You read that right, it's terrible and that's why I got the camera.

It turns out that it's so bad that some folks hacked it and made a firmware upgrade called Magic Lantern which makes the firmware awesome. I don't need an intervalometer anymore to do time lapse videos, I can bracket up to twelve images in a sequence of my specifications.

Are you using it for Instagram and Facebook? Then you don't need a big sensor. If you're using it professionally, or intend to, then consider getting something with a larger sensor.

Your camera will not survive caving without a proper box. Buy a Pelican case. Not everyone is planning on taking their camera caving. If not, this isn't for you.