My 2014 has the coils and I supplement with Firestone air bags. Overall, it's a great setup and very capable. Much stronger than the 3500 leaf springs alone - meaning if I pump my airbags up to 90psi my truck will sag far less than a 3500 with the same load. Of course, other things like axle and tire ratings that are stronger on the 3500 come into play. I'm talking strictly about suspension. Also, I never put anywhere close to the max in my bags. 40-50psi is more than enough to keep the truck from sagging under the +/- 3000# payload.
If money were no object, a Kelderman system like Crash posted would be great.
I tow an 11000# 5th wheel and with the hitch and things in my bed I'm usually close to the 3000# payload limit. Overall, I'm super happy with the setup since the coils ride much better compared to the leaf springs when not towing.