BY THE BOOK, I believe all of those work equally well. However, EP assumes your GM will runs a game based on reasonableness rather than pure rules. So with that in mind, we have several flying options: Ionic, microlight, rotorcraft, thrust vector, winged. Of these, thrust vector is the only one that should work in a vacuum. On the flip side, it will work the worst under gravity. Microlights, wings and rotorcraft will work the best in a high pressure, low gravity environment (and worst in the inverse environment). The big difference is some of them will be more sensitive to gravity (such as rotorcraft), and some more sensitive to air pressure (such as microlights). All of these will be built for a specific gravity and atmospheric pressure. Some of them will be more adaptable than others (wings are perhaps the most adaptable, assuming a good engine, since lift/drag are based on speed. The book suggests ionic drives are also extremely adaptable.) I really don't know much about ionic thrusters. Reading up, it seems to be more sensitive to gravity than to air pressure. I assume everything except vector thrust will be fully effective under 1g, 1 atmosphere. The next step is to also consider the additional costs. Wings require speed to operate, which limits operations in tight confines. Ionic turns air into plasma, which sounds pretty dangerous in a crowded habitat. Vector thrust are noisy and burn through fuel like nobody's business. Microlights are slow and have weight restrictions. Rotorcraft are also noisy and fuel hogs (although much less so than vector thrust). Note that I'm not a physicist, so I can only give general, ballpark information on what I understand to be correct.

It's important that you're comparing the Robot Winged to the Biomorph Winged, but yes: smaller things in lighter gravity.