My favorite character is Princess Twilight Sparkle. First off, I love her because I think she's very adorkable! She has a beautiful color scheme in my opinion. Also, I really like her because I can relate to her. I too am a bookworm, and I love to learn new things. Also, I like her before & after she got wings. I may be in the minority when I say this, but I think she's even cuter as an Alicorn!
I really like all of the Mane 6, though. Some other characters I really like are Starlight Glimmer, Princess Celestia & Luna, Silverstream, and many others!