I think both would be interesting to play as, but imo the Elites would be somewhat more challenging from a writer's perspective. Playing as the Failures basically writes itself---it would be a simple thing to come up with realistic, flawed characters and play them off of one another. But playing as seemingly "perfect" specimens and folding in more subtle flaws and undertones I think would be a bit more difficult, in a good way! 

So my vote's for the Elites. But both would be fun! 

If we're going for Elites, I've kind of come up with a quasi-character concept (still need to fill in the finer details). How about a character who is otherwise perfect (I mean in ability, not in personality), that is, despite passing all of the screening, diagnosed with a rare disease of some kind partway through the mission sound? Perhaps he/she could be playing some kind of important role, and would have hid his/her condition from the others. I think it would be interesting seeing how the group would contend with the situation, and playing as a character who must deal with its consequences/his own ineptitude. Or would that not work out? Tell me what you think!