Aries is the safest bet.
The other usual suspects will continue to be major players throughout 2013- Roode, Hardy, Storm, Bully, Kaz/Daniels, Joe, and Angle(if his health holds up). Anderson and RVD could still always play apart in the mix, but I suspect both have seen their final days as true TNA main eventers/world title contenders. Hogan and Sting will continue to get their usual large share of the spotlight too.
The other guy I expect to rival Aries as the main focus/success carrying the company in 2013? The old stand-by... AJ Styles.
I think AJ will get a big push through the summer/fall and get the same "retribution" treatment that Hardy got this past year. I expect AJ to win the BFG series, and win the title at BFG.
Hopefully we will get the AJ/Aries program that we haven't gotten since Aries' return to the company.
Someone in the X-divsion; like York, King, or a returning Sorenson or Sabin may be darkhorses to drastically improve their standing in the company as well.
Morgan is another guy that could get another push to the top of the card before the year's out, just to once again show how ultimately uninteresting he truly is.
Also don't count out a major impact being made by an outsider that hasn't entered the company yet- some potentially marketable Indy talent who enters via Gut Check(like Brian Cage for example) or via the Destination-X tourney if they bring it back. Or possibly a surprise WWE releasee who still has the capability to draw.