Just my opinion (and maybe that of my tiler)-- but when we renovated a bathroom that had a shower/tub combination (not a free-standing tub-- so against 3 walls)-- I went with a rectified porcelain, for both walls and flooring. For a shower that will get hit with water on a daily basis, nothing beats porcelain, in my opinion. Absolutely nothing can get through it. And because it was a rectified porcelain, the tiler was able to lay these 14" tiles with a very very narrow grout joint (something like 1/16"). Check out Crossville Porcelain. We used 'Generals Gray' from their Empire Collection. Polished on the walls and unpolished on the floor-- 14" floor tiles laid on the diagonal. Really some of the prettiest porcelain I've ever seen. We love it-- and relatively affordable. http://crossvilleinc.com/products/empire/

Natural stone or porcelain will work fine in your shower. Natural stone has the up keep of being resealed every few years but if you're using a polished stone you can get by without sealing. You can also purchase porcelain tiles that have a polished finish too.

@dianahb @CinarInteriors Thanks for your comments, all very helpful info.

With new HD imaging you can get polished porcelain that is almost impossibe to tell the difference between it and real stone. Just no added worries. Here is a job I recently did with products from Emser.