My Flutter app tracks games people have played or are playing and offers recommendations. I want to move user data, authentication and API calls to a backend.
I'm comfortable with Flask but haven't used Express in a while. Does Express's async model or its library ecosystem make it a better choice here?
I'd start with Flask if you're already confident in it. Knowing how to structure, debug and maintain the backend will probably matter more than picking up Express again just because it's an option.
Either framework can handle routes for a game library, authentication and calls to external APIs. Pick the one that lets you get those pieces working safely, then revisit the choice if you hit a specific limitation.
Express is worth considering if a lot of requests will spend time waiting on external game APIs. Node's async I/O model is a natural fit for that sort of work, though it doesn't make CPU-heavy recommendation calculations automatically faster.
Flask can call external APIs too. The practical difference depends on how you deploy it and how much concurrent traffic you need to handle. I wouldn't switch based on the word async alone.
I'd compare the actual packages you need rather than assuming one ecosystem is better overall. Check the options for authentication, database access and whichever game data APIs you're using. A maintained package with documentation you understand is more useful than a bigger package count.
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beyond-repairable:
What makes familiarity matter so much in the long run?
third drawer witness:
You'll spend time changing features, tracking down bugs and keeping dependencies current. Familiarity can make those jobs quicker and make it easier to spot mistakes.