I am sure that between the fabulous four(platies,guppies,mollies and swords)Mollies and gups are the more prolific.I can only say for what I've seen in my tank and my fish experience.I do believe that mollies take a bit longer in between and that gups drop every four weeks or so.Somebody had argued that mollies have larger amounts of babies but I hate to differ.I had this female half black blue guppy that would have at least 50 babies every time.Now my sailfin female molly would have babies not as often and about 20-30 babies each time.So you see.....I think the gups are the clear winner this time.
I would also would like to add that I think there's no other species of fresh water fish that mate so often as a male gup.The stamina they have.Who needs Viagra when you have the sex drive of a male gup.