Which are best backlinks for indexing?

Hello, I am creating FIVERR gig for indexing backlinks and I see many gig like "I will build backlinks with 100% Index"

I want to create same gig but need to know which is best backlinks for making sure Google Index them?

I know free way to help index backlinks just do not know which ones are best to use.

Start of by using massive sites that index super fast like Reddit and Medium. Find all the sites like that and I'm sure that list will be long enough to start selling on Fiverr or whatever freelance site.

So far I know WORDPRESS.com, bravesites, Medium, REDDIT, Blogspot do index fast and easy but I need more for completing Fiverr gig. Any help?