[khuzudin]

Why not both? If you’re selling new puzzles for your puzzle app, you can let users buy individual puzzles or themed puzzle packs as one-time IAP, and also sell subscriptions which give users access to all puzzles you publish while their subscription is active.

[amichail]

What if the game has 100 levels?

[smoldesu]

I don't really think it matters, this site has seen a lot of studies studies showing that iOS users will pay money hand-over-fist either way.