I, personally, prefer the net breeders. I believe they allow more water flow into them, they seem to have much more space then the plastic ones, and easily attach to the side of the tank. The only thing I had trouble with is remembering them when I did water changes. Have to be careful not to let the water in them get too low.
This, of course, is if you are going to isolate a fish or put fry in there. If you need it for a fish that is ready to give birth, I don't recommend it as the mother can easily get to the babies.