Well the M923A2 has power steering, full air brake (which can be a bit touchy) A bigger cab and it is quiter inside. It also has super singles on which can be taken either way as an advantage or not. another big issue is the truck is heavy. i think around 23,000lbs or so empty weight and it is over 26,001 lbs GVW. Legally you can not drive one with a class C in PA no matter how it is registered. I know this is going to bring up a fight, but ask Penn Dot or a LEO. Parts might be a little bit of an issue right now, The M939 parts will become more availalbe as time goes on.
The m35a2 has manual steering ( which as long as you don't have to parrellel park it is ok), hydraulic brakes (which work pretty good if in good working condition, Wheel cylinders and master cylinders will leak if there are damaged seals.), the cab is smaller, not an issue on short hops and it is louder inside. The up parts in my mind is the manual transmission which if a gear starts to go bad you can get around it so it is harder to kill. and the ease of parts and knowledge on the trucks. I don't think you can stump this board on a M35a2 question. And there are alot of aftermarket parts to get as well. You have dual 9.00 - 20 tires which you always have 4 spares if needed. The truck is lighter at 13,000 lbs and a GVW of 23,000 on road. There is also a wieght tag for on and off road. the M939 does not have an on road rating, just off road.
The CUCV is just a diesel pickup truck. pretty standard, 14 bolt locker in the rear, 6.2 diesel, 400 th transmission. Alot of info is on the board about these as well.
So the M939 can haul 10,000 on road per the data tag, the M35a2 can haul 10,000 on road per the data tag and the M1008 can haul 3,000 or so. Not 100% sure about the data tags.
Bottom line is personnel preference. Take a look at all 3 and decide from there. If you are around central Pa I can help you with that.