I pee sitting down because I lived by myself for years before getting married and had to clean my own bathroom. My aim was fine but the splashing made a bit of a mess.
One of old bosses had five (5!) boys and was building a new house. This led to a discussion about putting a urinal in one of the bathrooms. Didn't happen and am curious to hear if anyone has considered it.
My husband sits if at home. He is tall and does it to avoid splashing/making a mess. It works for us because I never have to worry about a lid up. We are teaching our sons both ways.
My DH is a typical guy (i.e. not a metrosexual) and he sits at home. Interestingly, the only times I've notice he's stood up at home, is when he's really fired up and annoyed about something at work. lol I think there's a correlation (like, "screw this! I'm not sitting down!")
I pee sitting down only at night at my doc's suggestion after I passed out after peeing standing up a few times. Apparently, I have a condition known as micturation synchope. It's kind of funny actually. Haven't had an episode since I started sitting nearly 20 years ago.