Most office and public restrooms (for men) have a ratio of 2:1 or 3:2, urinals to stalls, from my estimation. Sitting down isn't an option when there's a line.
You just wait.
Not always feasible. The brilliant designers of my office gave us a total of 8 urinals/stalls for the men on this floor (same for the other floor, approximately). The ratio here is terrible, about 5:1 men to women (probably worse, actually). There are 200 of us on this floor, 800 in the building. The after lunch bathroom rush means you stand around uncomfortably while waiting for a stall, or use a urinal and get back to your desk.
I guess it depends on folks. Usually i plan my bathroom visits outside of the rush hours and i dont wait to have to pee to go. This allows for more flexobility but again maybe not everyone can do that.
I do sit. But those guys I know who refuse to sit, do so on the grounds of manhood. Sitting is not manly. Obviously.