At the moment I currently don't have a "main." I mained a Paladin at the beginning of MoP, but after I unsubbed I got a few classes to 90 but none I can really see myself maining in the long run.
Though my current plan is to, after I level this monk to 90, main it as an alliance character in WoD, and boost an Orc Warlock for my horde in WoD.
Which one I will really "main" (as in actually raid on, be geared etc) remains to be seen.