Humans
Ai – My favorite character by far. It's a shame that she seems go unnoticed, even by the Mewtwo fans. Yes, on the surface she appears to be a bland character, but there is much more to her. She had wisdom beyond her years ("Life is wonderful…"), was selfless, devoted, and warm-hearted. (Oddly enough, she's the only character who I call by the Japanese name.)
Ash – He's spirited, ambitious and compassionate. Unlike other heroes in stories, he is far from perfect. He has his faults, such as getting cocky at times. I like that he is an approachable character.
Melody – I love that she's a priestess! (I forgot her actual title.) I've always been a sucker for priestesses/oracles/etc.
Sabrina – I don't know why I like her. I just…do.
Molly – Here is a child who was tormented by losing her parents, caused turmoil, and ultimately took the responsibility to fix the situation.
Miyamoto – I don't like her as much as I used to, but…eh… she's funny nonetheless. I think it's the purple hair. I love purple hair on bishies.
Domino – Being a Mewtwo fan, I should hate her, but I don't o_o In fact, I don't know why I even like her.
Aaron – Aaron is a lot like Ash. He is another hero, but still has faults. His faults are not as apparent as Ash's, though. Anyway, I like Aaron a lot, and I think it's influenced by the fact that I adore Lucario.
Pokémon
Mew (8th movie) - Okay, I'm sort of biased here. I have been a Mew fan since 1998, so it was only natural for me to like the 8th movie Mew. Without getting into too much detail, I ended up liking this Mew more than the one from MSB. I realized that the one from MSB really didn't DO anything. It said something harsh to Mewtwo and than fought him, but that's it. The 8th movie Mew, though, just seemed more… important.
Mewtwo – I think I'm the only person who prefers Mewtwo when he was a child over his adult form. While I must admit that I AM drawn to Mewtwo's philosophies, it gets old after a while. But young!Mewtwo is so innocent, curious, and so on.
Lucario – He's like Mewtwo but not quite as angsty.
Pikachutwo/AKA Pikachu's clone – He's spunky :3
Ash's Pokémon - They all have distinctive, interesting personalities. I'd talk about all of them but I'd be here forever, so...