Depends on how much of the back window you're willing to block.
If you stay below the back window in the SUV I'd say the full-sized car has the edge. But if you block some, or all, of the back window the SUV gets the advantage.
If you have no more than 5 people in your party I'd say the full size car has plenty of room, Unliess you overpack.
I drive a Ponitac Grand Prix (approx same size as an Impala) and we have no problems brining luggage, etc for a week-long trip for 4 (two adults, two teens).