First, decide how you really want to use your truck; do you want a lift just for looks or will you actually flex it?
If you think you will go off-road for weekend fun/getaways, overland adventures, wood chopping trips, or any other reason to hit ranch or mountain trails for fun, work, etc., avoid any spacer lift and especially the ReadyLift 3.5 systems (read their fine print).
If your weekend off-road fun includes some moderate to more technical four wheeling, avoid the cheaper drop bracket lifts like Superlift, Tuff Country, Trailmaster, Rough Country, Zone (cheaper version of BDS), etc. as they are all priced cheaper for a reason (Chinese-sourced materials with inferior production quality and/or American-made but with thinner spindles, cross member brackets, weak UCAs, etc.). I had to stop on trails for a few owners of such equipped vehicles that needed help after pounding their vehicles some. But if you're sold on drop bracket lifts, you may want to consider some of the better systems such ProComp, BDS, FabTech, etc. (which I have also used before the coil-over systems were offered) but they all have their pros/cons as well.
If you're not going to beat up your truck for fun or work and just want a mall crawler, then going with a spacer system is ideal since you can add larger tires and get that more aggressive stance that is so popular with the truck crowd for a lot less money. I have done that a few times myself too and really liked the stance I was able to achieve (although never at 4-inches). I think I like the ReadyLift SST system for that reason since they also come with UCAs that allow you to get your factory geometry almost back to factory but still attain almost 4-inchs of lift; the downside is that the ride will be stiffer since you will be preloading the springs but you'll hardly notice that if just street driving (assuming your streets are relatively smooth). Higher speed handling will also suffer (compared to stock) due to obvious result from raising your center of gravity.
If I didn't routinely hit the desert or mountains where I live, that would be the system (or the Rough Country equivalent) I would pick for the price. I appreciate
@Nick@GotExhaust comments mentioned above since those systems will serve you well as a street truck with better ride quality than a spacer system but I would personally avoid any drop bracket systems that requires cutting/welding of factory components on my truck unless they were proven to be top shelf (which Superlift and Zone are not); but again, they would not be cheap.
