This is another personal preference thing and note that all silvers are not the same.
My fave is 1z Pro MP topped with UPP, but my wife's fave on the same paint is Souveran, and a number of Autopians prefer Zaino or KSG on the same paint! Very different looks but everybody has their druthers.
FWIW, I found that BF darkens silver quite a bit (noticeable when you compare side-by-side with another car having the same paint), UPP less so but still a little. Both gave me decent depth, a lot more than some other products, but it was the prep that really made the difference, even on pretty new vehicles. Most people don't see the little flaws that detract from silver's overall appearance- that's the blessing and the curse of that color.