Metric (SI) vs Imperial
I'm American and I prefer the metric system and use it as regularly as I can. I started using the SI units when I took high school chemistry during my sophomore year (2 years ago) and I finally started understanding it when I took AP physics during my junior year. It makes much more sense since it uses base ten instead of random numbers. However, I still have to use the imperial occasionally since most Americans don't understand 30m but they understand 98.5 ft.
So, what country do you live in and which system do you prefer?