H.I.I.T. stands for high-intensity interval training. It is a highly intense workout that alternates between intense bursts of activity followed by periods of less-intense activity.
M.I.S.S. stands for moderate-intensity steady state cardio. It is a steady, challenging-but-manageable pace that is longer in duration than H.I.I.T..
If you answered "yes" to all of these questions, we would recommend H.I.I.T. cardio for you. If you answered "no" to any of these questions, steady-state might be more ideal for your needs.