All springs settle, even OEM, but lots of folks in my opinion get hung up on the stance (rear-end up/down in relation to the front). Frankly, I dislike rear-up being higher, ok to be a smidge higher or level. However, it comes down to what you do with the truck and how much time/mileage. The core question I ask and/or focus on is are you bottoming out ever, sometimes, a lot, or all the time. Obviously, want to be level or little below level if towing, but again whether towing, offroading, or heck even pavement driving are you bottoming out? Believe me, on my Jeep, I've had Jeep coils settle and weaken to where I'd bottom out over rail road tracks or transistions from tarmac to concrete when driving over freeway overpasses where there are often raised lips/curbs where at 65mphs an hour I'd hit bump stops. Not fun.
So this is purely your personal tastes at play here. To get a spring that will never settle is almost not possible; however, possible with such a stiff spring that you'd would never want to drive it. Even those overly stiff springs will settle with nominal use or sitting on the vehicle's own weight. Obviously, the more the springs cycle the settling effect accelerates. So figure out how much weight you carry on average or will ever carry (Max). Trick is to find a happy balance because not all of us leave 500-800lbs of weight 100%.
My rules of thumb to determine which springs to go with are:
- Determine the weight you been carrying: average & max
- Unloaded height (Stock, +1, +2, etc.)
- Duty cycle (time) of the above 'max' noted above: Is that max weight 100%, 50%, or etc.
- If 50 or 100% the consider going HD version of said height
- Then factor the above three items on how much settling you'd tolerate
- If your OCD will cause you sleepless nights then factor in one or two inches higher(if 50-100% of weight range the same for HD); so that, after settling you'll be right where you want to be