I think EMD had a real winner with the GP35/SD35 body style: economical to produce (virtually no curves!) but somehow uniform and harmonious: they stuck to it with minor revisions up to the early SD70. Their current production... looks like a home-built, put together out of spare parts. GE... I have the sense that on a very small number of occasions GE has looked at its locomotives, found them messy, and called in a designer to clean things up. (B39-8E/C39-8E marked one occasion: cab looks disturbingly, umm, Spartan, but the whole locomotive is much cleaner than the Dash-8 designs.) But they don't do this very often, and between "designer-interventions" design changes are allowed to accumulate in an uncontrolled way, with looks getting wartier and wartier over time. The "classic" U25B was a sculptural masterpiece, but none of the later U- and Dash-7 bodies were as clean.
...It pains me, as a GE fan, to say this, but I think EMD locomotive design, until the last decade, was usually better from a purely aesthetic point of view. Even GE seems to have imitated them at times: the cabs and noses on the W-1 electrics built after WW II for Great Northern were clearly designed by somebody who had looked at EMD's E3 through E6 passenger diesels for a long time!