At this point, at release, I'll playthrough the EA section with an origin character and see what playing as one actually entails, before deciding who I'll be during the first playthrough.
Having Gale's commentary is always nice, and there's so much Shar material to be found in the EA alone, that Shadowheart is already a semi-permanent member. The free spot can go to anyone, maybe Wyll just to see the Mizora angle at the Towers.
I would say there are some origin characters who have a very present personality and there are ones who seem more open to different, let's say, alignments. If I'm playing as Lae'zel, it'd be very strange to act like some magnanimous do-gooder, and I'm interested how the game will reflect her non-PC personality as you're playing her. How will the game react to a Lae'zel who prioritizes helping the Tieflings before finding the creche?