Mace/Pepperspray is less effective when people wear glasses or other kinds of eyeshield.

I suggest a high power flashlight, such as the ones made by Surefire. Just in case you were to 'spray' someone by accident, a super blinding light is less painful and doesn't last as long as the spray might. And flashlights have longer range, so you can do it when they're far away.

While the person is blinded, you should have enough time to run, kick-in-the-nuts or whatever. Plus, a flashlight has more functions than self-defense.
Those surefire ones are super bright. I haven't had the misfortune of having one shone in my eyes, but I've seen the beam they produce when compared to other flashlights. I'm sure it would work.