What is your goal?
The main goal of HIIT is to get your body to naturally release more HGH (human growth hormone), which signals your body to burn fat and build muscle.
Most research papers I read found shorter sprint intervals and longer jog/walk intervals most effective. The easiest way I found to do that is to sprint (100% all out sprint) for 100 yards (or 70 yards up hill)(should take ~15 seconds on average, a little less on the first circuit a little more on the last circuit) then walk slowly back to the start and repeat 6-8 times. If you are truly sprinting at 100% effort you should feel a great tightness in your chest, like your lungs are about to burst after the 3rd or 4th circuit. You should be involving your entire body, arms pumping as hard as you can, etc. and feel a good pump in almost every muscle in your body. You only need to do this 2 times a week to get good results.