Speaking of workout vs diet... your diet is so much more important.
A while ago, a co-worker of mine was doing the new Orange Theory workouts and told me I could try it out for free. I did and it was a SENSATIONAL workout. I wouldn't call it HIIT, but it was close to that and was a lot of fun. I bring this up though because they wanted to get me to join (ofcourse!). I told them though that their prices were not justified for me because I already know how to get a good workout in and more importantly, yeah you can get good workout in and burn 750 calories in a workout. However, you can then go sabotage that by eating a burger, fries, and a shake right after. And I have seen this all to much. People think they can "reward" themselves for a great workout. No... you fucking can't. Not if you want to ever be in shape. You can always out eat a workout.