I've always had handlebar mirrors (Zephal), for years and on several different bikes. Finally, I couldn't take the sloppiness and the constant adjusting, and realized it was really distracting me.
Bought a mirror that hooks on my glasses (CycleAware) and really love it. Took about 1/2 hour to get used to it. The field of view is awesome for me, it doesn't go out of adjustment when I go over bumps, and it doesn't block my view.
I'm much happier with the glasses mirror. Your mileage may vary.
"If Americans want to live the American Dream, they should go to Denmark." - Richard Wilkinson