I like Monk a little bit better; not a big fan of the rune system for dks, it feels really limiting. Unlike Warlock or Shadow Priest for example where you can dot all the things and do crazy dps.
In regards to Monks I only played the Mistweaver spec seriously, the main problem I had with it is that you can't really choose who you want to heal effectively (Renewing Mists). I hope they fix that for WoD, but besides that it's a really fun class.