Springs: Variable rate OK?; Moog, Spicer, Husky or Acdelco?

[robroy]

Good morning!

Does anybody have opinions on whether variable rate coil springs are a good idea for our trucks?

Am I correct in thinking that the stock springs are fixed rate?

As for the brand, I see Moog, Spicer, Husky, and Acdelco. Any opinions on which brand makes the highest quality product?

Thanks folks!
-Robroy