Rancho 5000s were my go-to shocks for many years. They are inexpensive and simple, and they are hydraulic. Or at least they used to be. (EDIT - unless they changed, I'm sure they are still hydraulic. It should say in the listing notes)
I have since switched to OME or Bilstein shocks, which are both gas charged.
Difference? Hydraulic shocks are generally softer and smoother, but gas shocks seem to be able to handle quick changes more easily. Gas shocks also add height, while hydraulic shocks do not.
I would use hydraulic shocks on anything that will see off-road use, and gas shocks on trucks where road manner are the chief concern.