Kitty, Mrs Rose, Sam, Blaine, and Puck

Sam - He was a big help to Blaine in this episode. And his impressions were spot-on.
Artie - Wasn't much of him, but he was still funny anyways. Loved what they did with his costume.
Beiste - Once again, another inspirational scene done by the lovely Shannon Beiste. Brava!
Becky - Hilarious as hell. She was so cute with her costume. I'm glad they put her in this.
Brittany - Same as Artie, wasn't in much of the episode, but she was still funny, especially with that doll head near the end. And her costume was beautiful.
Mrs. Rose - She and Burt literally should be tied for the Parent of the Year award. Her talk with Jake was really nice. And even though I wasn't in the scene myself, I still felt like I was there defending her.
Jake and Puck - Props go to Puck for the brotherly advice, and Jake for getting Ryder some help. Really sweet of them.
Joe - Once again, funny as hell. His costume was really nice. Loved him in the opening scene, and him defending Mrs. Rose (with Artie, Ryder, and Becky) and singing in SN was awesome as always. Yay for more character development!
Tina - Her lines were funny as well. Of course, Blaine/Klaine stans may hate her for that, but you know; haters gonna hate, right? Plus, what she did at the end with ND was sweet.
Sugar - Her costume was beautiful, and her in the opening scene was funny, of course.

Ryder - He's really grown on me in this episode. Not the fight part, 'cause I thought that was bogus. But he...well, his vulnerability really showed. And when he said that stuff about his parents not loving him, I felt bad. It kinda reminded me of Dave in OMW a little bit. And now he's gonna get the help he needs, so that's good.

Honorable Mention:
Finn - He started off kinda...you know, clumsy, I guess, with the leading thing. But then he helped Ryder with his situation, and the tension between him and Jake. Plus, I actually liked a little bit of his leading as the episode progressed, and what ND did for him at the end. So...yeah. Yay Finn!

Finn or Ryder, basically for the exact reasons @fetchgirl2366 just said pretty much agree with her whole list.
Also, I'm surprised at Kitty being a favourite in this episode?

just him or Ryder maybe... I liked Artie, Sugar, Joe, Tina, Brittany, Becky and the rest but they haven't a great storyline in this episode, so I'll pick Jake because he really grows up helping his "enemie" and treating Marley and her mom like they deserve, I'm glad for him :)

ps: I loved the Sebastian comeback! he was awesome too, I just whish he would be a bitch again or at leas sing or appear more...

Definitely Sam. He's funny but also helpful to Blaine and he tries not to get bogged down by drama. I also liked Jake and Ryder a lot more in this ep.

Sam and Ryder were awesome during this episode