What kind of grout to use when tiling bathroom?

Since there are many features of grout, this will depend on your question.

There are epoxy grouts and latex modified grout. Epoxy grout is very stain resistance. The problem lies in that epoxy grouts are hard for a novice to use.

Latex modified thin-sets are durable when used correctly.

Additionally, you need to make sure you buy sanded or non sanded grout depending on the size of the grout joint and type of tile.

If you have many natural stones, glass tile, or a tile with a great deal of shine, you will need a non sanded grout. Many bathrooms need this regardless, because their grout joint is 1/8" or less.

All joints larger than 1/8" require sanded grout. This means you must be cautious before you begin, you place your joints correctly for the style tile you have.