I really liked Li Li. She's such a spunky little turd and her voice acting is really good. The pandaren child model is creepy-looking as all hell, though. I liked Fish Felreed's gossip text conversations, too.
I love Taran Zhu. He's a (Panda) completely out of his element, trying to maintain control over a situation that is far beyond him. He comes off as arrogant, condescending, and an asshole, but he wants what's best for Pandaria, and in his mind, that's an absence of the Horde and Alliance. He thinks he can fix it, but honestly he's in over his head. The threats Pandaria have faced for generations are serious, but isolated. He's in over his head and fighting it the whole way.
Lorewalker Cho is wonderful, endless stories to tell, and lessons to be learned from him!
Also now with the Timeless Isle, being able to speak with Emperor Shaohao has been really interesting, after watching the Burdens of Shaohao series
I became quite attached to him and I'm really glad he has more of an in game presence now.
Also Taran Zhu is just a badass!
I agree with Li Li Stormstout. Would have liked her commentary for all of Pandaria instead of just Valley of the Four Winds, but it probably wouldn't be a good idea to drag a child through those war zones.
Lei Shen was a good villain considering how new he is.
I thought Taran Zhu was an ass during his appearances pre-Shado-Pan Monastery, but he got better.
Lorewalker Cho, my favorite storyteller. I will be disappointed if he is restricted to just Pandaria. I would love for him to come along with us and tell more stories about the world around us.
Chen and Li Li Stormstout. I would follow these two across the world in any manner of adventure. Really fun, I think these two showed the lighter or brighter side of this expansion.
The Celestials were really cool. I felt questing around their respective temples and personally meeting these god-like creatures. My favorite moment was Yu'lon believing we the heroes) were the reason the mists parted. So we could come to Pandaria to play our role in destiny.
Lorewalker Cho. I missed him in ToT (admittedly he doesn't fit into that raid) and I'm really happy to see him back in SoO once again. He's the only dude who doesn't have some sort of anger issue, he's simply a nice panda.
Taran Zhu. I used to hate him with a passion, but his development from when he's first introduced in Jade Forest all the way to when he drags Garrosh away in chains at the end is amazing. Without a doubt he's the most deep Pandaren character introduced.