Personally I didnt Pair them up on the premise of which ones werent compatible. My choice for equiping them came on what skills they gave my characters. IE: Trying to get junctions on all stats. By the end of the game my summoning was down to Domtrain, Diablos, Cerebrus, and occasionally Eden (Though the long summon time annoyed me (yes i know you use it to boost them, but it got too repetitive)). That in mind i didnt really care about there compatability with my character with the exception of those 4.