Big dots as well as the small big dots are ok but don't waste your money if you like accuracy. I am talking scored qualification type shooting.
I picked up some TruGlo TFO's and I really like them. They are easy to see when it is dark and very easy to see in daylight.
One negative is that it is very difficult to rack the slide using one hand with them. The rear sights don't have a "catch" that can be used to rake it against a belt or holster like some of the other sights.