I'm a fan of wizards (as you might guess by my handle) so of course I'll be playing a mage first, but I'll probably try all three classes at some point.
I see the trailer as being pretty pointless as that didn't appear to be game play footage, and it really didn't reveal much except for classes we already knew about. We have no idea how much those classes can be customized, and how much versatility is in them.
Interestingly it seems like they have shown videos of Hawke throwing spells while fighting with weapons in melee in some of the trailers, this does make it seem unlikely that anything like that has been implemented into the gameplay though, except perhaps as an Arcane Warrior type spec if it still exists.