I haven't been playing for a huge amount of time but here is what I have.
Brewmaster Monk is top tier, they would be a strong class without Guard (build defense, get offense) but it puts them over the edge. Most players on the forum would strongly advise against playing them because of how strong they are compared to most other classes but it wouldn't be fair to you to at least not warn you that these guys exist. Windwalker monk is considered a fair but strong class here.
Rogue is where they have been at low lvl's since I have started playing, high burst damage stealth class. If you like preying on the glass cannon users and standing on even ground with a lot of the more balanced classes, go with the rogue. Combat seems to be the most popular spec here.
Paladins are next, they have a 5 second stun, decent heal, and OK damage. Not sure what spec is the best here, I have seen a little bit of everything. I would say paly and rogue
The last two I haven't seen too may of. Shaman I have seen mostly resto if I see them and all the locks I have seen so far have been really under geared, they have fear by this lvl and it looks like you get felhunter (if it gets rid of shields at this level, it seems really good).
I'm going to have to add Ferals are Stupidly over powered as well. They have a 3-5 seconds stun out of stealth and can crit upwards of 3k if they are geared enough. balance hits hard too and now it has an Aoe Silence that combo-ed with a pally stun or any stun or movement impairment might as well be a arcane torrent.
Shammys are Good heals
Holy pallys are better heals
Disc priest are better than holy pallys.
Resto Druids have more suitability than Disc priest just because they can get out of snares and have travel form.
Warriors do amazing damage not as overpowered as brewmasters but they can be good if enchanted correctly or played correctly. PS: Brews are only good once they get guard, if they are lvl 20 brews, they are pretty easy to take on in bgs. Arms warrior does more overall damage, Fury looks cool as hell but I feel it lacks rend and thunderclap that would make a difference in most fights.
Shadow priest are pretty much really squishy, brew masters. They hit hard as hell but they die fast as fuck if focused. Shadow priest dots tick for so hard its rediculous.
Ret pallys are under Spriest depending on the Ret pally. You need to be really geared. I mean geared like my pally, link in Sig. To even stand a chance against a spriest.
Rogues Take out everything except Ferals and Brews. They should be able to 1v1 spriest 1v1 pallys and 1v1 warriors 1v1 hunters if they catch them after a disengage, maybe even after they get one cause hunters are so bad in this bracket.
Hunters are the worst but right now have pretty high skill cap I think, only because a good hunter can take out warriors and ferals. At 29 they become harder to kill with their long range cc.
Elemental Shammys they are alright damage in EOTS they are nice to kill people off mid or lumber mill in Arathi and maybe the bridges in Alterac Valley. Useful right?
Enchanced Shammys, good for purging i guess never see any ones that grab my attention, never played one never seen one win many duels except maybe against Warriors.
Warlocks, Skill based class. Learn it love it, play it. Don't like it, don't play it.
Prot pallys Suck
Holy priest can be used for that stun but overall suck. They need that disc bubble what ever its called. I'm not looking up all the spells "Disc" is better tho.
K cool
,Duo out