if you have to ask - gas.
diesels aren't less expensive to own, they do get marginally better mileage and Wayyyyy better towing mpg; but today's gas motors are easily capable of 200-300k miles before needing major repair.
mind you - I LOVE diesels and own several... but unless you have a purpose for a diesel... no. With that said, the new light-duty truck diesels are interesting - but whether it GM or Nissan (cummins), the itty bity diesels are too new to make an opinion - especially since the TDI vw diesels have lots of troubles.
so, since you asked, why a diesel - if you're towing a lot, they get 2x the mpg of gas and have more torque so you'll run faster over hills (unless you turn up the wick, then you'll get the same piss-poor towing mpg as gas).
diesels really aren't more reliable because they're smog-encumbered, and gas motors have come a long way in material science... to the point that diesel-level compression ratios are coming in the next couple years to gas motors (with the benefit of more power for less fuel). Overseas, diesels make sense because the fuel stays stable longer than regular gas - here, we add cow pee to make them burn cleaner, but then decrease the fuel economy so the system stays hot enough to work....
for overlanding, a hot cat is a good way to start a fire... not a good thing.
Old diesels.... are awesome - no smog, mechanical pumps, stone-cold reliability, 0-60 measured on a calendar, noisy, smokey.... imo perfect.