I'd sit whenever possible, especially if I was all dressed up. Only once was I glad to have a penis because I had on a nice outfit and the port-a-potty was absolutely filthy inside. Wet floor, and almost everywhere else wet too.
I intentionally had my last stand up pee on June 9 2015 at 3:30PM before heading into the operating room. After that, well sitting is now a necessity but no regrets.
Love,
Clare