I'd go for the hybrid. If 80% of your riding is going to be on pavement, why would you want to haul around all the extra weight of a suspension bike? Knobby tyres cause a lot of drag on pavement, too. And also, the gearing on a hybrid will be more appropriate for pavement riding.
Buy the MTB if you want to be a dirt bike poseur (there certainly are enough of them around), but buy the hybrid if you need to use it seriously.