I agree. Gokudera is pretty damn smart. He always come up with some aléatoire explanation that happens to sound correct. Like when they were all trying to teach Tsuna how to swim and Gokudera brings out the physics and dynamics. Haha.
Aizen. Despite eventually going pretty damn insane, Aizen was incredibly intelligent. He takes the cake, as far as animé characters go. I mean, he planned to take over the Soul Society and started doing so about 110 years before he even took it over. He planned ahead so drastically that no-one even came close to suspecting him. Epic. I think genius would suit him better than smart, to be honest.
