Okay you will have to make up your own mind as to which is for you. They all have pros and cons I do disagree with Jeepsinker on the driveline availability though for the A0 and A1 parts are everywhere but the axles on A2s are different and therefore more expensive and harder to come by. The older 250 is as said super reliable and you can find anything needed to keep it on the road. I am a mechanic and love them all but they all have some drawbacks.
939A0 cons
Heaviest model of all
Slower
Doesn't have that big tire look
May not have ABS (most will)
Oldest of the series
Intermediate drive shaft in between transmission and transfer case is hard to maintain and is expensive to replace
Pros
More torque (almost as good as 809 series)
5 spare tires
Cheaper tires
Tires weigh less easier to handle
Over all less things worry with (no turbo, no CTIS, fuel system is not as finicky, no o-rings in wheels)
939A1 cons
Heavy but less than A0
Less torque than A0
O-rings in wheels tend to leak
Tires cost more
Tires weigh more
Truck is harder to get in
Intermediate drive shaft in between transmission and transfer case is hard to maintain and is expensive to replace
Pros
Faster top end but the tires are limited to 55 so should be better mpg and less wear on motor.
Bigger tires(so better ground clearance, better approach and departure angles, less ground pressure)
939A2 cons
CTIS (parts are expensive, hard to find, and is a complex system that most do not need or ever use)
Extra parts to remove when changing tires, you need more tools
O-rings in wheels tend to leak
Tires cost more
Tires weigh more
Truck is harder to get in
8.3 has turbo that needs to be taken care of or will be expensive to replace, and the fuel system is picky about air getting in.
Less torque than 250
Pros
Lighter
CTIS (will automatically keep tires at full inflation, I love the system when it works)
Faster top end but the tires are limited to 55 so should be better mpg and less wear on motor.
Bigger tires(so better ground clearance, better approach and departure angles, less ground pressure)
8.3 is great little motor and can turned up easily, parts can be found easily
Intermediate drive shaft in between transmission and transfer case is easy to maintain and not expensive to replace