I am a contrarian to the HIIT benefits for CARDIOVASCULAR health. This is based purely on anecdotal evidence...not supported by science (yet). I have personally known 3 close friends who suffered heart attacks after/during HIIT training. All were in their late 40's. All were in good shape (on face value). 2 died, 1 lived. Here is my personal belief (not supported by science but it makes sense to me):
We are all blessed with the flight/fight response to threats. We can do amazing things such as run lightning fast when being chased by a lion or lifting a semi-truck if your kid is trapped underneath. IMO, this response is designed to be tapped on rare occasion. For example, my jeep can go up to 110mph. But if I regularly drive it at 110mph the engine will blow. Much like our hearts. We can race them up to incredible levels in a fight or flight situation. But if you continually do it, several times per week, your heart will blow out, just like the engine in a car. Sure it CAN work that hard, but SHOULD it? You are purposely putting yourself in fight/flight mode by going all in on HIIT.
The same theory could be applied to bodybuilding, but instead of looking at the heart muscle, lets apply to the skeletal muscle. In a fight or flight situation COULD you deadlift 1000lbs to save your child pinned under a car? YES. Should you then try to deadlift 1000lbs several times per week? Hell no.
I would say the best cardio training when considering risk/reward would be weight training (actually a moderate form of HIIT if you think of it) along with lower intensity steady state exercises such as taking a brisk walk, walking stairs, or riding a stationary bicycle.