Looks like a run-of-the-mill D16A6 in the first pic. Not great for fuel efficiency, not bad either. The gearing sucks for FE though. (Trust me on that!!)
The front of the white Rex looks decent. Tough to say about the rest of the car because you can't see it behind the door and the guy.
The yellow race car doesn't look to be built for top-end speed. They want downforce, because that helps lap times more than low drag.
I don't know what to say about the silver Rex. I somehow doubt that the body mods are all that effective in reducing drag, but I could easily be wrong on that. At the very least, they should have covered the rear wheels in preference to the front. Doing both would be cool, but I don't know if reducing the drag from the spinning wheel is worth the extra frontal area and extra sharp curves and such.
The Prius is a Prius...
I would suggest a body that at least roughly follows the teardrop template seen elsewhere on this BBS. Make the upper part of the body narrow smoothly (in a teardrop fashion) as it goes back. The 1st-gen Insight and the old MX-3 do this to some extent, and there's a newish Volvo out there that does as well. You still keep the rear track where it is, but you can get better aero on the top ~third-ish of the body.
In general, the rear of the car is more important for aero than the front. But the front is important for
looking aero, so yo probably won't want to ignore any part of the car.
-soD