I found the problem with Ui is that she's so perfect and good natured that everything she does ends up being completely predictable. It really detracts from her character, because you're never surprised with her. This stems entirely from last season when she was able to impersonate Yui and play the guitar better than her with considerably less practical experience. She is like a certain other sister from a certain other series that shall remain unnamed. From the amount of food she cooks to the home run, nothing is surprising. In fact, the most surprising thing was that she played the organ in their "jam session" rather than a second guitar. I guess that means should could replace Mugi with little difficultly too!

Azusa definitely stole the moe fest this time, though their friend Jun was pretty good too, like a calmer, lazier Ritsu.

Thus:
Azusa >> Jun >>>>>>>>>>>>>>>>>>>>> Ui