I'm with agksimon on this. As long as you're shooting in daylight or on a normally lit range, I like the fiber optic sights, front and rear, preferably in different colors.
I use the Williams Fire Sights on two of the range guns, and these work very well even in dim light. On my M&P 40 slide, also used for home defense, I use the Truglo TFO night sights. They don't stand out quite as well as the Fire Sights, but they're a lot faster to get a sight-picture with than the standard sights.
So far, I haven't actually changed the sights on my shield, but I did make a vast improvement by filling over the white dots with florescent nail polish, red in the front, and green in the rear. I'll probably eventually put on the Truglo TFOs, but for now the bright nail polish works just fine on the range.