Half ton is a half ton for the most part payload wise unless you find one of the F150s with the max haul pkg. claim 3klbs payload but I don't believe it. They are heavier sprung than the others though. That said unless you're hung up on not exceeding OE payload capacities there are many econimical options to stiffen up the rear suspension, maybe more limited on the coil spring Ram 1500s.
If you're looking used for a truck then any of the bigger V8s or Ecoboost is gonna have a good tow pkg and miles and condition and price are more important than having the lower axle ratio of the max tow pkgs but having 3:73 or 3:92s does help in the hills. With the 6-8 speed autos now and high revving engines the axle ratio isn't as important as it used to be with 3-4 speed trans and half the hp.
If unite looking at Ford, wait until the new models come out. That should drop the value some on the current gen pickups.
Of the big 3 and Yota there is not a bad truck in the bunch now. I'm not a Ford guy and I'm partial to the 5.0 though. Good little pulling motor in my '11 F150. The newest Gen Hemi though is tops for hp and close on torque to the ECoboost.