Hmmm...that's a toughie. Some are favorites because they "wow" me and some because they make me laugh. Don't think I could name just one...so, in no particular order.
The Wicked Witch of the West (The Great Movie Ride, DHS, WDW): She's just extremely life-like and creepy. I love how it feels like she's looking at you when she isn't talking. She just looks around all sinister like...great stuff.
Big Al (Country Bear Jamboree, MK, WDW): A sentimental favorite, he always makes me smile, plus I love his song..."BUH-lud on the SAD-del"
The Caretaker (HM, MK/DL, WDW/DLR): Just always loved him...he's so scared and his knees are knocking...just funny.
The Hippo (it's a small world, MK/DL, WDW/DLR): Can't help it, think he's cute with his head shaking back and forth.
The Seagulls (Finding Nemo Submarine, DL, DLR): I just like 'em..."Mine? Mine? Mine?"
And finally, the Auctioneer (Pirates of the Caribbean, DL, DLR): I'm not sure if he's used to test new stuff at both DL and WDW, or just one or the other, but I like him regardless. I can recite all his lines. I only listed the DLR version because I just can't stand the WDW one after riding the original...its so much better!