It depends. The taller the dolly, the more leverage you will have. I've owned all three sizes. the 72" was a pain. it barely fit in my car, I had to move the passenger seat all the way up. The biggest problem with the 72" are staircases that have walls at the top, hard to maneuver. However, maybe this is just for your house and you don't have that. Maybe you have a truck that can haul it fine.
If it's JUST for pinballs, the 60" is probably the best. It can very easily haul a pin, and the handles are above the cab, no problems.
I currently own the 66" and that's the best for me. I think it might make hauling arcades easier, it fits well in my car, if I can maneuver a 72" with walls at the top of stairs this should be much easier, and it as more than enough leverage (not that the 60" didn't either).
My 2 cents.