I think the type of cardio is dependent on a few variables. If I am just in the off season, bulking, I just hop on an elliptical for 20min 2-3 times a week at high intensity. If I am dieting on a keto I would vouch for a L.I.S.S. (low intensity steady state) form of cardio below 130bpm as I will have no glucose to burn up and high intensity would go after muscle. Also a few weeks out from a competition I would be on a stair mill (stair stepper if it's not available) to really bring out those striated glutes.