Austin Aries is one of the best heels in the world. This is not even a question, anybody who watches TNA knows this.
However, he should have remained face for at least another year. I don't like that they turned him heel for the sole purpose of handing the title to Jeff Hardy at Bound For Glory.
However, everything about him just screams natural babyface. He's short, so he's inherently an underdog, but he's such a hard worker; he almost quit wrestling at age 33 or 34 until TNA picked him up, he really is a great redemption story. If anybody has seen his matches lately, you might notice that he does stuff like his corkscrew moonsault a lot less because he can't be "flashy", he's a heel now. He was over as hell as a babyface, and he really was one of the coolest characters in wrestling as a cocky face who pushed himself to the limit to get where he is.
Listen to the pop at 30:07
and 31:00. The guy was over as hell as a face, he's still getting pops in the UK much stronger than the heels, and IMO the guy is a natural babyface. I understand that he's a great heel now, but he was better as a face.