For me it has to be Steven or Blue. Blue is a real psycho ***** to fight, and that music only raises the nervousness that you know you are gonna get your ass beaten. And in fire red when you rematch him he is probably the most psycho crazy man in the world. As for steven, it took me soooooo many tries to beat him when I first went through ruby. Especially since my strongest pokemon was my lvl 100 swellow.