Midna. She had personality, and an interesting backstory. Zelda had personality, too, and she was helpful when possesing a Phantom, but the stupid rats scared her. Fi, while having the personality of a computer, was very helpful, while Midna and Zelda didn't give you very much good advice. I didn't hate Navi as much as some people do, but her info on enemies was limited, and rarely very helpful, and when I was doing side quests or looking for pieces of heart in OoT 3D, or even in the middle of a dungeon, If I had been playing long enough, she would yell "HEY" just to tell me to go to the next temple, or "We have to save Zelda!" or tell me to take a break.