6. Classic Doctor Strange (Marvel Comics)
Current Doctor Strange is a shadow of his former self, which is why I have specified the classic Sorcerer Supreme version of the character. The classic version of the character was nowhere near as physically strong, fast or as durable as Superman, but he could defeat him in a one-on-one battle by virtue of having an automatic forcefield powerful enough to withstand anything the man of steel can physically dish out. From within that forcefield, Strange can then cast a wide variety of spells to defeat the Kryptonian - which will definitely work, given that magic is one of the things that he is by no means invulnerable to. For example, Strange could cast the Crimson Bands - a magical restraining spell that wraps around its target and has been used to hold characters as physically strong as the Hulk himself. Also, from the safety of his forcefield, he could let out his astral form and ruin Superman's day telepathically from the astral plane. As a sorcerer who draws his power from a variety of massively powerful entities, such as the Vishanti (Hoggoth, Oshtur and Agamotto) and the Octessence (Balthakk, Cyttorak, Farallah, Ikonn, Krakkan, Raggadorr, Valtorr and Watoomb), the list of spells at Doctor Strange's disposal that could ruin Superman's day is almost endless.