Emma (Jayma Mays) might just be the best bet. She is fair, but firm. She isn't always great at managing people, but like Sue, she has shown a lot of maturation. Plus, giving her the position would open up a story for Sue to accuse her of favoritism, and give Emma some good episodes battling wits with Sue, something we haven't seen. So my vote is for Emma!
Glee's "Goodbye" may not rank among the best episodes of the series, but it is pretty good. Even if the music and plot is, at times, weak, the emotional heartstrings are played by a virtuoso. I look forward very much to season four next fall, and the changes it will bring!