for low intensity long duration cardio i would use a stationary bike or walk at 3.0-4.0mph on a high incline for 30-50minutes

for HIIT training i would use a stairstepper, elliptical or stationary bike and do this
5minutes warm up
1min at 40-50% of max effort
30sec at 85-90% max effort
1min at 40-50% of max effort
30sec at 85-90% max effort
continue that for 15-20 minutes or until you can't go any more
then cool down for 5 minutes

low intensity will burn more calories from fat but will also burn less total calories as the intensity isn't as high as HIIT

HIIT training will burn a lower percentage of calories from fat, though not by much, i think the study i read said 10-12% max, but will burn many more calories total and will increase metabolism for up to 24 hours after cardio, this is called the afterburn effect, where you burn extra calories because of an increase in metabolic output

to give you an estimate i wlll outline one of my cardio routines

low intensity
3.2-3.5mph 8%incline on treadmill for 30minutes burns 350cal

HIIT
using what i outlined above i burn close to 500cal in 20-25minutes plus the extra that i get afterwards