I cant vouche for single speed, but fixed gives you a certain amount of control that I could never achieve from a geared bike. When I used a geared bike I rarely used more than 3-4 gears anyway, so why add all the uneccessary weight and components that could just cause more mechanical issues? Most people find a gear ratio that is perfect for them in most situations, so its convenient to not worry about constantly shifting or having derailer issues. I never really understood the rage behind fixed until I gave it a go, but now I will never go back - its too fun.