If you happen to like metal or acrylic prints and live in the US, I would recommend Bay Photo. I don’t happen to like metal prints very much, but I have used Bay Photo when I had a need for metal. I have carefully inspected acrylic prints made by other astrophotographers using Bay Photo and they were excellent.
I haven’t used Bay Photo for paper prints since I prefer to print at home on a nice Baryta surface when making paper prints. But, at least for metal or acrylic for astrophotography Bay Photo is a solid choice for US residents.
Oh, my first choice for media is actually Baryta surfaces on either cotton rag or alpha cellulose. I grew up on paper, I’m used to paper, and I know how to get the results I want on paper, so that’s what I prefer. Most astrophotographers would disagree with me, though, so…