I personally wouldn't say that guppys/platies/mollys are the easiest to breed cause tbh I don't class it as the owner/keeper breeding them. If you have a male and female in water then in a few weeks you WILL have babies. And often you'll end up over run...
Now if you're asking what's the easiest egg layer to breed... that's a different story. Personally I'd stick to egg layers as they have a resale value. For livebearers you tend to end up getting stuck with a load of unwanted fish... unless you wanted to line breed a rare type?
guppies are the easiest of all livebearers to keep and breed
mollys also
guppies are the easiest of all livebearers to keep and breed
guppies are the easiest of all livebearers to keep and breed
+1
Although my Platies are breeding like bunnies!
Livebearers are all fairly easy to breed but hardly produce more fry than egg layers. A guppy may drop 30 fry every month or so but a well cared for egg layer will produce fry every couple of weeks if you move the fry along to a separate grow out tank.They will also produce fry by the hundreds at a time. People will constantly talk about how livebearers can overpopulate a tank but that is only because they can literally breed with success in a community tank in many cases. If you set up a breeding tank and separate grow out facilities, you can probably produce 10 times the number of things like convict cichlids from a single pair of adults.