I was also in the Closed Beta 5 for Aion in North America. This time, I focused on the foibles of the Spiritmaster (Elyos side), and it's been fun so far. This time around, I also focused more on the Crafting system, and I really enjoy it. I already ordered the Collector's Edition a while back, and I'm hoping there will be a solid following with Aion.
I hear you on the "What to play when the game goes Live" dilemma. The great thing about the game is that we have the stigma system as well as the ability to slot manastones, godstones, etc. into gear that allows it, so even if you're a certain class, you can tailor it to your play style. The crafting system is amazing, in my opinion. It's not too complicated but it isn't simplistic, either. It depends on how much time one invests into it, and it can be VERY rewarding, especially in the long run where mana/health/speed/flight potions are integral in PvP.
I've played all the classes up to level 25 (and higher) except Spiritmaster, and for me, it's a hand-toss among Sorcerer, Priest, and Templar. I love the spike damage of the Sorcerer class and when paired with say, a Priest in the Abyss, it's an amazing duo. I love the the fact that the Priest class isn't the typical "squishy" class, has great survivability, and is always an asset. Be prepared to be targeted first! I also dig the Templar's solid, front line tanking abilities, then again, a Gladiator with a Priest behind him/her is always amazing as well. I read in a recent article that the Gladiator has even more skills added to their arsenal.
A Chanter is a great class, a nice hybrid, and I've played/dueled some amazing people who know how to play that class. Much luck to you when the game goes Live!