A good question. Well i suppose there was no one better at that time to take on a hokage role and also the village and world were in turmoil due to war.
I watched the spoilers of the first season of naruto to be aired and i thought "let's see what this has to offer after Pokemon and Digimon and Beyblade." i Kinda liked it and continued watching uptil now.
Well both of them fought against Ichigo and Byakuya was definitely the hardest for him to beat so i'd go for byakuya. But then again kenpachi hasn't used his shikai or bankai and that makes more interesting.