Steve,
Your question will yield many subjective answers.

My limited exposure suggests the BSS and Winchester 21 doubles would be near the top in the strongest list. But, I could be wrong.

"Best" is quite a different bar to meet. I'm at a loss as to which makers would be at the top of that list other than some of the obvious London makers. But then, if you're talking about a target shotgun, possibly a Perazzi sxs would be in there.