Both can work effectively. However, volume has to be taken into consideration. As for HIIT, I would say a max of 2x per week. If you want to do cardio on other days, have it be low intensity. I'd suggest taking at least one day completely off a week as well (for most people this ends up being Sunday.) If you plan on implementing some form of HIIT, I would cut back on the leg training as well.
How about posting what you actually plan on doing? There's too many elements to consider to give a general recommendation.