Fit-Mommy is right, everyone is different and not everyone gets great results one vs. the other so you have to experiment. From my understanding, steady state cardio burns more cals while you are doing the activity but has little EPOC afterwards while HIIT burns fewer during the workout but has greater EPOC resulting in more cals burned after. I've spent years doing steady state and haven't gotten the results i've wanted since finally switching to HIIT this past month and dropping all steady state. However, I don't think this is because one is better or more efficient then the other, i think its b/c its something totally different then what my body was used to. I think its best to try and incorporate both into your program to reap both benefits. Just like when you find lifting a particular weight to not be as challenging you lift heavier to progress, the same is true with cardio. Doing just the same steady state and not pushing yourself will cause your results to slow. You need to challenge your cardiovascular system whether its by doing more time or more intensity. Hope this helps.