The easiest by far has to be platys or mollies. They pretty much seem to spend thier whole lives breeding if possible

You actually dont have to do ANYTHING to get them to breed, just 2 females ofr every male and it will happen. The thing with mollies is they can hold sperm up to 6 months at a time and you wouldnt even know they are pregnant for 6 months, then they start having babies EVERY month for 6-9 months!!! The babies i belive come out in about 10-30 (correct me if i am wrong people

) and you just have to feed them, there are foods in stores they will eat (baby fish pellets) because the babies are a good size. I work at a lfs and our mollies breed non stop, but never seen a platy breed, but i do know they breed a lot. Every week we usually have babies floating around, and we feed them Hikari Baby pellets, they love it, and the parents actualyl odnt tend to eat there young either, which is a good thing. So if you want osmething to breed then go with mollies, or platys. OH YA, one more thing which is actaulyl cool, Mollies breed no matter what, like i said before, but the thing is, they dont care WHAT KIND OF MOLLIE IT IS! a blakc mollie can breed with a pearl lyrtail, or dalmsation, or whatever! I dont know what the babies turn out to be like, we give our away when they are able to survive on there own (well in a school still though). Hope this helps

PM me if you have any more questions