Valving is up to you and how you drive. Stiffer ones will give a firmer ride with less roll, softer give a squishy ride that lets the springs compress easier but will bounce more.
Here is a site
that explains the valving
Basically the higher the first number the harder to compress it and the higher the second number the slower to stretch it back out.
For the front the simpliest is a 3.5" drop bracket or extension and whatever stock shock you like. Typically the fronts are valved high and rear lighter in a truck due to weight balance.
Personally I like a soft ride so my morning coffee doesn't go everywhere when commuting. On the beach though the soft shocks bounce everywhere. Depends where your priorities are.
My back lift is 6" so shocks are 28" ride height, 34" extended necessitating a 14" travel bilstein. 12" travel would work for a 4" rear lift.
Bilstein 5125 valving options = 170/60, 255/70, 270/56, 289/36
If I ever get around to changing the backs I am going with 170/60 which are super soft, more medium is the 255/70 and above that is comparable to the HDs. Its up to you what type of ride you want. Hope that helps!