I like so many of the characters, its hard to choose one, but if I had to, it would have to be R2-D2. This plucky little garbage can on wheels, whose entire vocabulary consists of beeps, has been one of my favorites since I was a child. He came to the rescue so many times in the movies at pivotal points(fixing the x-wing in ANH, fixing the hyperdrive in ESB, opening the bunker doors in ROTJ)that his simplicity of character is overwhelmed by his bravery and loyalty to his friends.