What Height is the best

[Leper]

It really depends on what you are going to do with your truck and how nice you want it to look. True, the lower the better, but that usually involves cutting up the body. If you are happy with the 6" and 35" tires, especially from a looks-only standpoint, go with a 6" rear spring. It is by far the easiest/fastest solution. Shackle flips are nice, but they are a more involved process than a spring swap.

If you decide you want a mud only truck you need lots and lots of lift and tire speed. The opposite is true for most trails and rocks.