again, I'll say the bilsteins. on my 2004.5 I installed bilsteins at about 10K miles. the difference was dramatic both loaded and unloaded. The factory shocks IMHO aren't valved well for either unloaded or loaded riding. The bilsteins are still working well on the truck (now our sons) at 200K miles.
When we got our 2015 I put bilsteins on as soon as I could get them. again factory valving on the stock shocks wasn't what I liked.
In both cases I used the HD yellow units. there is a firmer set for lifted suspensions or larger tires which the claim is a stiffer ride with stock suspension. I think the HD yellows are a 4500 or 4600 series while the blue units are the 5100 series.
