It really depends on the fish you are trying to breed, some fish are more "parental" than other fish. I'm not sure how neons raise their fry or take care of thier eggs (if at all) so you should probably look this up online. You also need to look up what conditions your kind of fish will spawn in, some fish spawn when frsh water is introduced to the tank, or when the water temperature is within a certain range, etc. Most of all, you need to be sure you will be able to take care of, or find people to take care of the offspring.
A seperate tank for the fry would probably have the highest survival rate without the negatives of a floating breeder (inhibited growth rate)
On the other hand, a floating breeder, while it may cause the fry to develop more slowly is not alot of work, and will have a high survival rate for your fish.
I however do not seperate my molly fry from their parents. If you want to use this method, it probably has the lowest survival rate, you have to worry about your filter sucking up the babies and the parents or tankmates eating the eggs/fry. Ways to overcome these problems are to:
1- Cover your filer intake with a sponge, nylon sock, or something else to keep anything from getting into your filter that shouldn't be there and works great for sand as well.
2- Put plants in your tank. Java Moss is great for covering parts of the bottom and is easy to keep. I am a big fan of duckweed, it will provide cover at the top of your tank (which could potentiallly block light from other palnts) and is out right hard to kill.
3- Don't keep predatory fish with the ones you are trying to breed.
For some fish this is the best method because the parents teach thier young.
