In canon the Michaels is Bernadette who is the top earner and generally never wrong about anything and is never ridiculed or slapsticked, though Sheldon and Amy win the Nobel Prize so it ends up being a rare triple Michaels.
Outside of canon, the main draw was probably Johnny Galecki fresh off of Roseanne though obviously Kaley Cuoco mogged everyone.
In an entertainment perspective, Sheldon is the clear Michaels since without him the show falls apart.
