How they compare
The difference here is how you pay. OnlyFans is subscription-based: you pay each creator monthly for their feed, messages and extras. ManyVids is a store: creators sell individual videos, so you buy exactly the clips you want and nothing else.
OnlyFans has by far the most creators, but finding them on the platform is hard; you usually need to know who to follow. ManyVids has a huge clip library with store-style browsing, and it's especially strong in niche content.
Each has its cost trap: subscriptions add up across creators on OnlyFans, and paying per clip gets expensive on ManyVids if you buy a lot.