Grout or Caulk in shower?

Non sanded grout is the way to go.

At least that is what I would do, then seal the grout a couple of times.

Wherever there is potential for movement you should caulk. If your entire bathroom tile job has a thickset (mud) job on seasoned wood, you probably could do without the caulk (I personally would caulk it anyway). If your tile is on anything else, caulk those corners and transitions. It's the recommended method as per the Tile Council's guidelines.

Look at it as cheap insurance. If you use color matched caulking you'll never notice a difference.

I use caulk in areas where dissimilar material has been installed. Example: a tile wall shower with a fiberglass shower pan.

TP

It might depend, in part, on size of surfaces and likelihood of movement. I recently redid our shower stall, only because one wall was getting pitted and didn't want leaks. Original tile job has grout in corners and base-to-wall. Walk in shower about 40" square with tiled pan and walls up to ceiling. Hubby sealed it. Looks sooooooooooo nice (the tile, that is) :o)

I put a fine bead of caulk around ceiling of the shower and outside down the edge of wallpaper/tile joint just to keep the wallpaper on. The ceiling was replaced at one time and never caulked.

I followed instructions on grout package carefully and when I thought I was ready to grout, I ran my hand over the tile and could feel soap scum. Out came the razor scraper and off came tons of soap scum. I have scrubbed and used lots of cleaners on tile, so was very surprised at the amount of soap scum.

I was confused about which grout to use, because premixed says "not for wet areas" or something of that nature. I used mix-yourself non-sanded. Be sure to wipe off grout haze per instructions. God didn't make muriatic acid to take off your grout haze :o)