Hulk is indestructible, whereas Superman has several weaknesses. Kryptonite, for instance, leaves Supes defenseless and very mortal. And let's not forget how Hulk smashes anything in his path! He doesn't hold back punches.
Superman has taken down so many "indestructible" monsters before. Do Solomon Grundy, Bizarro and Doomsday ring any bells? And besides, Superman has other abilities. He can simply fly and toss Hulk into the sun.