Firestorm I guess. But Cyborg already has a best friend and that is Beast Boy. Plus if DC is going with that Captain Marvel is Cyborg's best friend I'll go crazy! Captain Marvel is like my favorite hero after Batman, Robin, and Barry Allen and CM already has best friends: Mary Marvel and Captain Marvel Jr. I would be so saddened to see this happen to Captain Marvel. That is if he gets his own comic soon and Cyborg is heavily featured.