If you are buying and not primarily driven by cost, get the diesel.
A dually does have parking issues, but even a SRW 250 is not simple to park in a typical restaurant parking lot, more so with the long-bed. I typically drop anyone with mobility issues off at the door and then drive out and park where it's easier. I count that as exercise!
The long bed makes manuvering easier with the trailer in tow in many cases and gives you storage space in the bed. Con is that is less manuverable without the trailer than a short bed.
The dually vastly upgrades your pin weight capacity. Con is parking.
The diesel pulls better and is more economical running with the load. It has no cons but the cost IMO.