The ratio of CHO vs fat being burned through activity is irrelevant. If it mattered, then the exercise most prescribed for fat loss would be hanging out in a coma for 3 months. Carbs that don't get used become fat. If you use the carbs in your system, then there won't be anything to feed your fat, nor will there be much circulating blood sugar, so you'll either have to eat more or break down fatty tissue for energy to replace the sugar that's been used up.
So, really what matters is how much energy you burn in a session, and how you behave outside of the gym (your eating habits and your non-exercise activities). If HIIT means you can only train for, say, 20min, while aerobic training means you can go for an hour, aerobic training might win out. If you can get the same over-all duration of either, then the finer details will determine what's more appropriate for you. If you're doing strength training outside of cardio, then aerobic training may be better, since it's usually less taxing on the body, especially low impact stuff like cycling or the elliptical. If cardio is your only form of exercise, then for the same session duration I'd go HIIT instead of aerobics.
Which is all one big roundabout way of saying "it depends."