Perhaps the only two possible contenders from the guest star list are James Spader (Boston Legal) and Catherine Tate (Doctor Who). Tate's character is completely unpredictable, changing her opinions constantly, but she is a friend of Jo's, and that gives her a leg up. Spader delights as a creepy salesman who insists there are no products to sell, just sex. His time on screen is short, though longer than the other guest stars, and it reminds viewers just how good he is, and how he should be back on series television as soon as humanly possible. Either Spader or Tate could fit well with the current ensemble.
There are also applicants from within the office vying for the position in front of the "search committee." Jim's favorite, and the frontrunner going in, is Darryl (Craig Robinson). Sadly, Darryl botches his interview, doesn't have a resume, ends up making a terrible resume, disappoints Jo, and resorts to cheap tricks with his daughter to try to win the position. Even Jim begins to look exasperated with him by the end. This likely spells the end of his efforts. Kelly fares worse, being laughed out of her interview almost as soon as it starts.
Andy could possibly be the new front runner. He is underwhelming, but as he says, he will not make waves or changes. Dunder Mifflin Sabre has been through a lot lately, and Andy's leadership style may be just what they need. Though not an early favorite, as Gabe goes on the attack during the initial interview out of jealousy over Erin, he distinguishes himself as he decides to really go for it. He is educated and qualified, and isn't contributing much to the company as a salesman. It could be a perfect storm, or lack of other options.
Dwight (Rainn Wilson) redoubles his efforts, determined to prove that he can do better than he did in his recent, brief stint as manager. He uses disguises and bribes to try to work his way into the top spot. Jim is dubious, and refuses to actually consider him, even after Jo asks him to. Considering Jim seems to be the decision maker, does Dwight still have a chance?
Or could Jim reluctantly step in? Despite Spader and Tate's memorable performances, The Office has such a large cast already, it would be good to keep it in house. Dwight is risky, at best, and Andy doesn't blow anyone away. While Jim is previously reluctant to stay manager after his run as co-manager with Michael (Steve Carell), perhaps he will try again, given the lack of options, and the way a poor choice would reflect badly on him and his career.