A few years ago when we moved from MT to NM we rented a large Uhaul moving truck. When we moved a few months ago from NM we used a large Penske truck. Both were the largest of the respective fleets.
The Uhaul truck feels like it has a larger packing volume than the Penske. The Uhaul was 23.5 interior feet plus roughly 2 feet of the "mom's attic" while the Penske was just more than a straight 25 feet. However, the Uhaul was 8 1/4 feet tall and the Penske was only 8 feet tall inside the loading area. I checked the respective specs online and the Uhaul is taller. Ok so the volumne for each is as follows, neglecting the "mom's attic", 7.67 x 8.25 x 23.5 = 1486 ft^3 versus 7.67 x 8 x 25.16 = 1543 ft^3. This was enough of a vertical difference that I could not fit my kids' bunk bed parts in a vertical upright position. They took up a lot more room lying down.
I appreciated the lower loading deck of the Uhaul and the extra height in the packing volume, as just mentioned.
On the other hand, the Penske truck had a diesel engine with a lot of power while the Uhaul was a gasoline engine that felt a little under powered. I could travel up Spanish Fork Canyon at 45mph at the slowest in the Penske but the Uhaul would only do 30mph with the pedal to the floor.
Both were automatic transmissions, so I did not have to worry about shifting in traffic. In both, I did use the gear shifter to force a downshift when pulling hills. The Penske exhaust smoked a bit until it warmed up, that was frustrating as I thought I has done something wrong. Also, I had to let the glow plugs warm before starting, for those not familiar with diesels this means you cant jump in and start it immediately, you have to wait for about 30seconds. Both companies treated me very well.
Penske gave me a timeline to return the vehicle without miles, while Uhaul gave me a timeline and a miles limitation beyond which it was some amount more money per mile (I felt that was a lot).
To Sum up: Both were great, I like the unlimited miles and more powerful engine (that matters going up hills and canyons) of the Penske but I liked the taller loading capability of Uhaul and the lower loading deck.
Now you know and knowing is half the battle.