Recently an older man saw my bike and asked, "Why are you riding a boy's bicycle?" I just shrugged and said, "Because it's a better design." I hadn't really thought about it.

Today bike frames are designated less and less by gender (although it is still very common), and more frequently as either a "diamond frame" (gents) or a "step-through frame" (ladies). The step-through frame was made simply to accommodate skirts and dresses and clothing that could easily catch on a cross bar—the equivalent of riding sidesaddle on a horse.

I originally thought a diamond frame was a better design because I think they look better aesthetically, but I learned that diamond frame bikes are also typically lighter and therefore faster as well as structurally much stronger.

I'd love to know: What do you ride and why?

I lean towards pre-war/mid-century classic repro bikes like the above:
Linus Roadster Classic, Schwinn Coffee 1-speed, Velorbis Student Balloon, Kettler Men's City Commuter.