all livebearers are easy to breed,
guppies are simply more prolific.
What is easy I say? I believe they both are pretty easy without exception.
Some things to consider.
Male Guppies only need breed once every 8-9 months to keep a livebearing female prego.
Male Platy's only need breed once every 6-8 months to keep a female prego.
Guppies give birth to around 75-100 for a large female per month. Huge fems can give birth to upwards of 150+ FPM.
Platy's give birth to around 30-75 FPM for normal fems and Huge fems around 100+ FPM.
Guppy fems give birth every 25-30 days.
Platy fems give birth every 28-32 days.
This is inclusive to SB's also so the mort rate is added in there.
Normal guppies live about 2-3 years for most people exceptional lives at around 5 years.
Normal Platy's live about 3-4 years for most people exceptional lives at around 6 years+.
This data is from my own 7 years of breeding all livebearers commonly found in LFS and online purchases.
Of course there are always exceptions to every base. I happen to enjoy them more than most other fishes and so kept very complete records back in the days I kept them.