You need to think about what you want to place there. Height of shampoo and soap bottles.

My tallest bottles are around 12 inch tall.

I'm not a niche fan. Too difficult to get the tile right. Complimentary shelves that drain and clean well are a much better alternative.

I agree^^^

I used shower baskets in the bathrooms of my current house. I had done niches before when remodeling, but wanted to keep things simple when we built a whole house.

Kartners shower basket; come in different styles and finishes.

I also placed them behind wing/pony walls so they are not visible unless you are inside the shower. I like not seeing the clutter when you walk into the bathroom.