I would prefer to take this question as: If I had free reign to pick someone that it actually
could be, but that I know it won't be. In other words, not considering contracted WWE talent.
With that said, I agree with scomvp.
My pick would be Kevin Steen.
Although there is no chance that TNA would ever have the ability to lure him off the indy's, Steen would be the perfect choice.
Clearly TNA will never have Stone Cold or Punk(again), but they could do the next best thing and get a guy who could be their own Stone Cold or CM Punk, and that guy is Kevin Steen. Steen showed, in spite of how badly Cornette booked it, in his feud with Cornette that on the right stage he has all the tools to be the kind of mega anti-authority star that Austin was, and that Punk was starting in the summer of 2011.
He isn't a bad fit for the group from a look or attitude standpoint, and he would give them a wrestler with the chops to fit at the top of the card, as well as the elite mouthpiece that has been lacking. In my opinion Steen and Hardy could have one hell of an entertaining feud over the World Title once Steen had been built to the proper level(which likely wouldn't take long because he is so good at knowing how to get himself over).
As a back-up choice, my other "not gonna happen, but would work better than what will probably happen" is for the president to be James Mitchell. Mitchell definitely has the look that would fit as the head man over a biker gang, and his ECW past makes him a logical fit with guys like Devon and Taz. They would need to have a wrestler in the secondary role obviously, but grabbing almost anyone with ties to both Mitchell's and TNA's past would fit the bill nicely. Someone in the vein of Raven, Vampiro, or even Abyss would all be logical complimentary peices to Mitchell at the top of Aces and Eights.