There are two main options available for the load space of a pick-up; open and closed top. Most pick-ups are able to haul about a tonne of cargo without causing excessive fuel bills, they are still more thirsty than an SUV though so if you don't need to carry as much you might want to reconsider.
With both single and double cab options available for most pick-up's on the market, it really just comes down to whether you need the 5 seats a double cab offers, or whether 2 will be enough.
Depending on how off-road you plan to go, you'll want to check the ground clearance, the higher off the ground it is the less likely you are to scratch or scrape it on uneven surfaces.
Most manufacturers will give you a wading depth for your pick-up, so if you regularly need to drive through water you'll want to check the depth won't flood the engine.