Some players did used transmogrification, some didn’t bothered. With a little bit of taste, anyone can setup their new gear to look better. For example, the hunter new arena season looks really bad, using transmogrification is not a bad idea.
Mostly everyone is trying to looks as shiny as possible using the most rare items, more shiny, but getting a great set might mean also to keep the gear within one or two main colors like red and white, just black, look like an undead, etc. Or use a theme like Demon Hunter, Blademaster, etc.
Here are a few examples for Rogue (also the logo for prettypls.com, probably one of the best transmogrification setup), some warriors, prot, fury with two swords, a fury dwarf with two Corrupted Ashibringers, the most wanted swords in the game even more wanted than legendaries because of the rarity and the transmogrification possibilities. Also a Mage and a DK gear setup.