The Great and Powerful Trixie. I love her bravado She's one of my better impressions, and I really like the feeling of getting into her character, feeling like I can do a good impression as well as act her. She's just so much fun.
Another one is Spitfire, who is probably my best impression. She was my first real voice acting role, and I've never felt closer to a character than I felt when I was playing her. There was a lot of sincerity in that particular script, and some of the best emotion I've ever done. I'm a little sad that so few projects need a Spitfire.