What's the difference between a public relay like Damus and a Paid Relay like Nostr.Wine, Which should I use? and which should I donate to?

If I post does it post to both relays? are relays essentially parallel instances? or individual networks?

So many questions so little do I know, how long can a note fit?

And If I post something here, is it reliably existing forever? i.e I can publically start blogging and build my business / journalism ? or are we still in beta state?