Which RV have the best aerodynamics? A, B or C?

Negligible differences....

It's more important which one has the layout you want for your RVing lifestyle UNLESS you are on the highway more than in a site.

This makes almost zero difference in MPG, as your tow vehicle "hides" the bottom part. Unless this is a theory exercise, this would be the absolute last thing to consider about rig choices.

Weight and if it can be towed safely by your tow vehicle first, floorplan, comfort, and ease of use/living is second, fit/finish is third, color and trim, after that.

If trailer companies wanted to make a more aerodynamic shape they would be better to round the back of the trailer. Most people don't understand that putting the air back together is more important than how you rip it apart.

Hi,

Class C is the worst from an aerodynamic point of view.

How deep are your pockets?

They're all so terrible aerodynamically that it just doesn't matter which one you choose.
Get what you like.

Doesn't matter much; its about frontal area and they are all rolling bill boards. Weight is more crucial and HP. More HP used equals more $$$.

Important question is
"Can you afford an RV?'

Fuel consumption is not the most expensive part of RVing.

Frontal are is about the same on all of them (including the Airstream) so they're all pretty much the same....

Without exact dimensions, the question can't be answered.

Frontal AREA is the thing that matters, especially with such similar units.