I love Tidus because he is light-hearted whitout being annoying and his lore of waking up in an strange world kinda clicks with we players that are also discovering Spira.
The one I hate the most is Vaan. I think we can't even say he is a protagonist. He is so random in FF XII that I don't even see why he exists, and less so why the game gives him so much focus when he doesn't add nothing to the plot.