In the absence of adequate muscle glycogen–as would be the case with a low-carb diet–I would have to say that the low- to moderate-intensity route would probably be best for you.
While I’m a strong proponent of HIIT, you will not be able to sustain adequate intensity with this method of cardio training in the absence of muscle glycogen. You simply cannot mobilize fatty acids–whether they be from intramuscular triglyceride stores or adipose tissue–quickly enough to meet the high-intensity energy needs.
In addition, in a state of glycogen depletion, your best bet is to go the aforementioned route. However, if you’re carbing up, then I would recommend HIIT for your energy system work early in the week (or however frequently your carb-ups are) until you’re relatively depleted. This is when you would commence the lower intensity, steady-state stuff.