I read many threads about how the 3-way fridge sips propane....and runs for ever using very little. I switched to a DC fridge a few years ago and was amazed at how long my propane tank lasts now.....so my 3-way was using more propane than I had originally thought.
I think the size and shelf arrangement is dependent upon what type of camping you do. My trips tend to be long....from 4 to 6 weeks in one spot.....so for me the largest fridge I could stuff in there make sense. It might not make sense for you. I started a thread about my install you can find with search. There were pictures comparing the old 3-way with the new fridge so you can see the shelf arrangement and see some of the measurements. The new fridge holds a lot more than the old one just because of it's design.
The DC fridge has been flawless for me and I would never switch back. My driveway is at an angle.....now I can just plug in to shore power and load up the fridge ahead of time when prepping. No more turning the pilot on and off while at the gas station etc., no more worrying about being at an angle, no more constant monitoring for temperature. Now I just turn it on and forget about it.
The solar keeps up with it generally.....but I carry a generator for those times when the weather is socked in for many days in a row. It's better to run the Honda generator a couple of hours rather than start up the truck and use it as the power source.
2010 Ford F250 4X4; 6.4 Powerstroke Diesel; Warn 16.5 winch; Airlift Springs; Transfer Flow 47 gal. fuel tank, BDS 4" lift kit, BDS dual steering stabilizer with upgraded Fox 2.0 shocks, Toyo 35X12.50X18 Open Country M/T tires, Pro Comp wheels; 2008 FWC Hawk Camper; 2000 Toyota Tundra.