I've always been the Mage type, or magical hybrid like a paladin, in every mmo I've played, so I stuck with Mage for AL as well. I haven't played any of the other classes yet though, so the only advice I can offer is to stick with the class youre always more drawn to as your main.

I've ended up making a character for each class, but never been into it as much to get good with them, but it's always good to have a character in each class in case a party needs one for an instance.