#4 Demon King vs Randy Orton
Two legends of the sport, two great performers, and two men who at the moment are slightly underutilised by WWE. Finn Balor has one of the best gimmicks in the WWE. The gimmick involving The Demon King really is unique, and is one of the few gimmicks that still holds a certain level of mystique.
The Demon King going up against Randy Orton who himself has shown on more than enough occasions the demented, twisted, and edgy side to his character. This could lead to a different kind of feud between the two, where it's the midgames that takeover and dominate, rather than the long boring monologues that are becoming the norm for the feuds these days.
With Randy taking a backseat from the championship feuds, and Finn hardly getting the push himself, it would suit both wrestlers to be embroiled in a feud with each other.