Who's your favorite, Mewtwo or Lucario?
Who has a cooler design?
Lucario , Mewtwo looks like a rip-off of Frieza and Giegue(from Earthbound) while Lucario looks like a wolf warrior.
Who's better in battling?
Who's better to play as in Brawl?
Lucario , he is more deserving , he is also a unique character in Brawl due to his ability to get stronger as he takes damage and not as light as Mewtwo.
What else about them do you think is better?
Lucario has the best Pokemon movie and there are people who agree . Mewtwo's movie is overrated garbage that doesn't deserve any praise , the moral "fighting is wrong" made it worse that it is . Pokemon is about creatures that battle each other . That's like having a Jewish vegetarian going to a BBQ and eating all the pork chops in sight.