Subway tiles are the most practical tiling around. They have been around for decades and never seem to look dated. They are classic! There are so many colours and textures around, but I always say go for white for the most versatile.
In the past few years the trend has been to do white grout with white subway tiles. It gives a super clean look, and feels really fresh. And if you install it yourself and have a few crooked tiles, it will camouflage those mistakes.
But why not try a dark grout now? Years ago there was one grout colour - gray - and today you have about 20 choices if not more by mixing some together for a custom colour. Now you can try blue, pink, orange, or even black like in this photo.
For the most classic look though, stick with practical, dirt-hiding gray. In my soon to be new bathroom, I will choose gray. If you follow my blog, you will be privy to all the finer details of that reno when it starts to unfold, white subway tiles and all.