Which is better for overall health, steady state cardio for 45 minutes 6-7 times per week, or 20 minute HIIT sessions 3 times per week? I'm also interested in other options that I didn't mention.
Now don't take everything I say at face value, but if I remember correctly, there is no definitive answer as to what intensity has the best health results.
However, for overall health, a combination of both aerobic (cardio) and resistance (weights) exercise would result in a better reduction of risk factors (such as blood pressure and body fat/waist circumference) than either aerobic or resistance exercise alone.
Current guidelines recommend 150 minutes of medium intensity aerobic exercise or 75 minutes of high intensity aerobic exercise paired with resistance exercise twice a week. However, that isn't to say that doing 300 minutes of aerobic activity and weights 4 times a week will not be better for you; after the guidelines have been met, the benefit from doing increased exercise will be reduced, but still increased. Let me know if this part makes sense or not because it's kind of hard to verbalize.
My professor always emphasized that people nowadays are too focused on the numbers on the bathroom scale. If your primary goal is to lose weight, be aware that a combination of aerobic and resistance exercise may not result in weight loss, in fact you may end up gaining weight. Even though you are losing fat through all this exercise, at the same time, you will be gaining muscle and thus may not see the weight loss results. However, you should be able to keep track of your progress through the monitoring of your waist circumference, which, through the course of the exercise regime, should continually decrease.