Don't let distance be the only factor. Load levels are also a huge consideration. If you are putting unloaded miles on a diesel, you will have some issues as well. A diesel engine needs a load in order to operate efficiently. Unloaded, the truck will not produce enough heat to keep the motor at peak efficiency. If you don't NEED the diesel for towing/hauling, the gas will be much easier on the wallet in maintenance cost and total investment. Typically the diesel will get the same mileage as the gas truck unloaded. It is only when towing where the diesel tends to get better fuel mileage.
But, if you just want a diesel to have a diesel...party on!