Depends on what you use them for as well as the intensity etc. For example, I do a couple of LISS 5k runs a week, purely for health and basic conditioning. Now, there's a 250m beast of a hill outside my home. Pretty sure if I built up to 2 x 10 sprints a week, I'd be fitter than I am now. Even though I'd be covering half the total distance.
It's not an and/or, it's a continuum. In the one end you have LISS which is aerobic conditioning, cardiovascular "health", ability to recover, development of oxidative enzymes, capillary density, oxidative fiber characteristics, eccentric cardiac hypertrophy and so on. On the other, you have HIT which is aerobic threshhold/anerobic conditioning, ability to dispose of lactate, anerobic fiber characteristics, power production and concentric cardiac hypertrophy. The two exist on a continuum and overlap at some point, but at the ends they do not replace each other.
You have to decide where you are on that continuum and what the sport requires. For any aerobic sport, sprints are a very useful supplement for performance, but the foundation is LISS. If HIT was what they said, then the Crossfit champ would truly the fittest man on earth.
You can do heavy resisted, high intensity, balls to the wall training from here and to eternity, but if your aerobic foundation and conditioning is not up to par, you will still not be fresh and recovered in boxing or MMA. You do not build up that system as effectively by doing HIT.
Best practice, which is both from evidence and clinical experience, has shown time and time again that the individuals with the ability to keep their conditioning throughout a fight are the guys who do not neglect their LISS work. It is as much about learning to control your output and put a sustained effort, as it is the adaptions.
