Basically, the Looted Wagon is comparable to a Razorback in many ways, but can exchange its transport capacity for a Boomgun, making it into more of an artillery piece. It also has a larger transport capacity than a Trukk, and the ability to fly (for all the looted Hammerheads and Devilfish out there).
Speaking of looted Hammerheads, here's mine, which I can't resist showing off because I'm still really proud of it even after all these years (I think this guy is about 10 years old now).
If I recall correctly, the writing on the side of the tank says "kill 'da humies". Also, I'd like to call attention to the fuzzy dice hanging next to the driver, and to the angriest Drone ever. Enjoy!