Shower back panel experiences, quality, joints?

Moreover, the options for tiles/grout are practically endless.

What do you mean by that? Grout is just grout, right? You should probably choose the darkest color possible so that it doesn't discolor, right?

Joints come in all colors and recently we laid very narrow ones (1-2mm) with anthracite grout in between. That causes no problems at all. Any other material in the shower, whether glass, metal, or similar, requires more work or needs more maintenance. We tiled with large formats 60x60 with these joints, natural stone look, and it looks both classic and modern. I can only recommend it.