As someone who always prefers making up "functional" old-style colour-matching transmogs (ie mail armour that actually looks like chain mail, leather armour that looks like something a swashbuckler would wear) I'll pretty much only be running Challenges when I'm bored with everything else I'm doing and wanna do something a little more difficult.
This is the kind of transmogging I prefer (pretend that my monk belt is actually displaying and the offhand isn't borked):
http://us.battle.net/wow/en/characte...Baroban/simple