If by aerodynamics you're meaning mainly in terms of air resistance when towing, as opposed to other considerations like stability in sidewinds, then pay at least as much attention to the back as to the front as a lot of the drag comes from there. A rounded front and a long pointy back, like a teardrop, is about the best overall form. Of course a tapering back cuts into the usable space inside quite a bit.
If you've seen the trapezoidal pyramid folding structures on some semi trailers, that is why they're there. You can safely bet the trucking companies would not install them without their saving enough fuel to make them pay over time.