Board Thread:Theories and Speculation/@comment-30355627-20170128224827/@comment-9782468-20170209182335

MInato clearly reacted to hit. He was going to jump. But at the same time, he would have been obliterated along with it. He didn't want that, because it'd take him out of the fight for awhile (he didn't know it'd legit destroy him for good). Tobirama just had the better option because he had a clone do it, so he himself could keep fighting.

Also, Minato had less time to react to it, because he didn't see it. Tobirama probably was looking at it as soon as Minato jumped back.

As far as speed goes, Minato is faster. And his use of FTG is apparently superior. Reaction speed is debatable.