[lunarhighway]

personally i think the first is better than the second, the angle of the rear is quite important, i believe up to 11° the air will stay attached but beyond that it will start to separate... wich is why certain cars with a low Cd such as the prius or the audi a2 have a pretty high rear, to not exeed this angle... the longer the car the lower you can have the rear. from the look of if the top drawing has a better angle that the lower one.

if you are going to cut into the body, try sloping in the side behind the wheels. the top profile is just as important as the side profile.

but don't take my word for it, as ther's people with more knowledge on the subject here