I only read the big cases since law school, so take this with a grain of salt -- I've only read one or two KBJ decisions and a handful from Kavanaugh and ACB.

In terms of legal clarity alone, Gorsuch and then Kagan are ahead of the pack by some margin, followed at some distance by Roberts and ACB. Sotomayor is great as a writer, but not in terms of legal clarity. I think Thomas is middle-of-the-pack, and I think he gets underrated in this regard because people dislike his opinions. Again, experience of Kavanaugh and KBJ's writing is limited, but they're at least not far behind the pack here.

Alito stands alone as the only one I'd say is bad for a Supreme Court justice. And that's relative, so it doesn't mean he's awful, but I do actively avoid his writing.

The variance gets way higher the further from SCOTUS you go. At the state level it's basically roulette.