Unfortunately, nobody.
First of all, they never have full confidence in a wrestler, nor do they construct a slow but steady build-up for anyone these days. One month, they will be pushing this guy; couple of months later, they will be pushing another guy; sometimes they give the World Title to wrestlers in a way to persuade them to stay back (Styles, Sabin, Sting in the past), or they try to imitate or capitalize on what is hot commodity in the WWE (Randy/Magnus, Authority/Dixie, Bryan/Eric). When the momentum wears off (less often), or they simply find out that people didn't dig that crap (more often), they move on to the next guy and it's an endless circle.
Stars like Bobby Roode, James Storm, Austin Aries and Bully Ray could have been much bigger if they were constantly kept in the main event picture, hunting for the World Title. Along with them, TNA had Kurt Angle, Samoa Joe, Jeff Hardy and Abyss. Total 8 veteran wrestlers in the upper-midcard and main event of a 2-hour show. More than enough. No need for any part-timer, no need for any Bellator fighter, no need for any stable trying to take over the company each year. Instead, they went with those worthless reigns from Styles, Sabin, Magnus and Eric- which didn't do anything for anybody. The current one from Lashley will soon follow the list. Everything is a clusterfuck, but there is still time to improve.
Also, their wrestlers lack character development and a backstory. There is no repackaging either.
Almost all of their wrestlers these days debut either (a) as a part of an existing stable (Knux, Snitsky, Ezekiel etc.) and their role is limited to that, or (b) carry forward their character used in another company (wrestlers from Japan, ROH or HOH) or (c) simply debut randomly and start fighting (mainly X-Division stars). They come and go, but nobody cares.
Apart from their wrestling skills, they don't give the audience much to care for, cheer for or to tune in for. Like J.R. keeps saying, their main strength is wrestling from bell to bell. But wrestling alone is not enough. You need an interesting character and/or a strong story for anyone above mid-card at least. Samuel Shaw has a character and story, he is someone worth watching. So is Ethan Carter III. 5 years ago, "The Pope" was an awesome gimmick and people loved it. EC 3 and Sam Shaw are valuable additions to the mid-card and could serve as main-eventers someday. But TNA being TNA will probably screw them up too.