I always use male guppy to female Molly. Let's just say that male mollies are big lads that do some serious damage to female guppies. I read about this subject many years ago and was generally surprised that so many people hate it so passionately. I personally see it as no different to parrot cichlids that frequent almost every LFS
I visit. You can get some very interesting colour and body morphs from the fry. I've been hybridising for a couple of years without any deformities (I get an epic amount of straight Molly deformities though) but the offspring are never fertile. I've heard rumours of fertile hybrids but mine never have been. Who knows, we may one day have a new viable hybrid species. The super immune sailfin muppy!!