I vote for the airbags.
2006 Rockwood 8315SS (Current)
2011 Flagstaff 831FKBSS (Just ordered)
1995 Chevy K1500 5.7L (Now sold)
2004 Ford Excursion 6.0L (Never going back to gasoline for towing!)
I added the complete rear Air-Rite system to the Chevy (Bags, Compressor, and auto-leveling switch). Made the whole towing experience better. (The Chevy was a little underpowered and close to it's max tow rating.) Handling increased, bumps were smoothed out, and I went down 2 links on the dual-cam.
When I traded up to the Excursion, I didn't need the leveling assist, but I missed the comfort of the extra support, so I added the same kit! What a difference.