Chalk up another "death to U-Haul" vote. They are, in the words of Jeremy Clarkson, "biblically terrible."
Penske, however, is smooth sailing. My girlfriend rented a small Chevy 1500-based box truck from them...no extra charge for one-way, no mileage charge (only pay for gas and rental fee), and the rental fee was cheaper than U-Haul's fee even before mileage costs were factored in.
And I, too, have driven the 26' International from Penske (work rents one occasionally when we have more than three pallets of stuff, because it won't fit in the Sprinter). The one we got had a floating bucket seat, and convex anti-blind-spot mirrors. But the steering wheel is ungainly, and the cabin can be charitably described as "somewhat loud." I have no doubt believing it will tow a double-car flatbed though. It may be slow, but holy torque. Anything that can carry 8 1600 lb. pallets of beer in the back and still move is good in my book.