Gurren Lagann, it's kinda obvious. Nobody can match Gurenn Lagann and his Space-Time Shattering Burst Spinning Punch. Altough Iron Man with Extremis would make a good deal ( he is kinda the Ultimate mecha Human Sized ). There is also Lost Planet Mechs that are kinda cools ( especially the one in the last part of the game ), and also The Viewtiful Joe Mecha Transformation (which is still in my heart for ever :D)