Thanks everyone. Sounds like it boils down totally to personal preference.
To be clear (probably more clear than the original post that I wrote while slightly distracted), I was not asking about the aesthetics (by themselves, or relative to our house), but if one has a nice advantage over another for a garage/workshop & it sounds like even that is mostly personal preference.
I've usually thought of casements as single pane, relatively modern windows, but slightly ironically we have a classic MCM ranch house with mostly huge, multi-pane wood double hung (mostly can't be opened) windows and a few tall/narrow casements on the end. The windows for the garage will also be multi-paned so generally match what is predominant on the house (wife's preference, i'm ambivalent) so the only aesthetic differences would be screen inside/outside & a larger center divider for double-hung.
So, aesthetics aside, my thinking is:
Casements probably win. Screens on the inside mean I can leave them out a lot of the time which is nicer since I don't like screens. I guess I can put a fan in a window for either type & they are in a location where I doubt casements would cause much grief for people outside the window then they are opened. They are enough of a wash cost, aesthetically & efficiency-wise that it comes down to function as the only difference.