For the fronts, most people go with Bilsteins. They do not have them listed for the Armada but the ones listed for the Titan fit. IIRC, they have two models, 5100 and HDs (the latter being non-adjustable). I went with the HDs and thought they made a good improvement. Definitely reduced the bump steer.
However, I think most people replaced them when their front shocks were shot so some of the "OMG they are the best things since sliced bread!" reviews should be taken with a grain of salt. I replaced mine at 43k and they were better than stock but not OMG better. A good upgrade though.
Another thing to look for with squeaking is the front anti-sway bar bushings. Those can make a squeak / clank over speed bumps and the like and are cheap from the dealer. If you don't feel like replacing them you can squirt some lube in there like PB blaster which will last for a little while.
As far as the rears you'll have to do some searching. I have an LE which has the rear auto leveling so no good air bag replacements as of yet of which I am aware.