The problem with tiles that are in at the moment is that they will look terrible in 10 years.20 years ago it was all ceramic,a lot of swedish white 8x8 then came marble,granite and slate followed by glass and handmade.At the moment I would say it was funky glass and metal,anything that some designer thinks is in.It will all look outdated in the future,even the classics even if they do have a better chance.
The only advice I could give is that the client should pick their favourite tile that fits with their house.
Surely 'fashion' is good for trade.... It goes out of fashion, the client wants it updated with the latest 'in' tile......... Can't be bad.