There is no longer such a thing as rated arenas for twinks. This website does however have a skirmish rating pulled from the Blizzard API. Skirmish rating works as it does with endgame rated arenas. There is however a twist to it. At endgame, the MMR tries to face you vs teams with similar MMR. In skirmish, the game priorities quantity of games over quality. Meaning, that you face completely random teams. However, if your skirmish MMR is significanly lower than the opposing team, then you will gain a lot of skirmish MMR. And vise versa, if you lose vs a skirmish team that has low MMR, whereas you have high MMR, you will lose a lot of MMR. So in that regard, it is just as it is at endgame.
Here is the ladder:
http://xpoff.com/wow-ladder/
A level 19 is fairly easy to level and gear. Most of the gear consists of BoA's and quest/dungeon items. Look at the 19's directory for more information on that regard.
US directory:
http://xpoff.com/threads/the-19s-directory.59340/
EU directory:
http://xpoff.com/threads/the-19s-directory.66240/
As to what classes are the best. For arena, DPS classes like Warriors & Monks dominates the bracket. Simply because of how easy and effective they are at this level. As for healers, Disc Priests and Rshamans seems to be the choice.
However, if you are truly looking for a challenge, try play non-fotm classes. If you are a good player, you should still be able to beat the bads that queue fotm classes. However, should you meet good classes in the hands of good players, the match becomes incredibly hard, which in my opinion makes it interesting. I dislike the easy wins, and savor the hard matches, win or lose. Also, a win just feels that much better vs fotm stuff, when you play underdog classes.
It is important to note, that 19's at this moment is a lot more about the Gulch (WSG), than it is about arena.
GL twinking.
