It comes down to cost in my opinion.
If you don't mind throwing some serious coin at the 9" and are ok with having all custom parts its a great choice.
If you want cheap and beefy and the ability to find parts in any junk yard in the country then a 14 bolt is a better option.
Another axle to consider is the ford 10.25.....they are similar in strength to a 14 bolt but have way better ground clearance
09 Dodge 2500 w/ a Cummins, dd/towrig
85 Toyota Pickup, 1tons, coilovers, 40's, ect