IMHO, the smaller (Doodlebug/CT100U) has more of a vintage look, just because there weren’t many “big” minis being made at the time, and those that were looked different from the CT200U. That said, if you’re going for comfort as an adult-sized person, the 200 is a better choice. You also won’t have to swap the engine out, as they come standard with a 196cc clone engine. The anemic engines the Doodlebug and CT100U come with almost guarantee you’ll want to swap them out for something more powerful.
If you do manage to find an actual vintage mini, I’ve found them to be much more work (due to corrosion and needing refinished), usually missing essential parts (like wheels, seats, controls, engines, etc), and obtaining parts will usually be less straight forward and certainly more expensive. Not to talk you out of it, because I still grab every reasonably-priced one I can get, but if your goal is to get riding ASAP, and have something a bit easier to deal with, the Chinese bikes might be your bag. Or get a Chinese bike, then keep your eyes peeled for a vintage model to add to the collection…