All three specs are viable. Brewmasters make strong FCs and anti-FCs. They have 25% damage reduction, 20% increased stamina, and they stagger 20% of incoming damage which is all good for flag carrying. You also have a ranged spammable snare, which is great for keeping people off you as a FC as well as slowing down EFC and EFC's support. You also have Clash which is sort of like Death Grip and it stuns as well as spinning around the target. This can really mess up the EFC.
WW monks deal strong damage and have a damaging stun on a 25 second CD. They have good mobility with a base 10% increased movement speed (stacks with minor speed boot enchant!), Chi Roll + Momentum talent, and Flying Crane Kick. Similar in a lot of ways to a rogue or feral, but you lack an interrupt or self heals and stealth. The main thing is the stun, get a healer to around half then Fists of Fury = dead.
Mistweavers can stance dance between dealing out a bit of melee damage and healing. Your healing is pretty simple but you can be interrupted easily while channeling your main heal Soothing Mist. If you want to roll a healer you'd probably be better off going Paladin or Druid.