Hello. I'm using DropBox API and DropBox .NET SDK to implement an ability to export files from our application to user's DropBox account (using standart OAuth 2.0 authentication). The code is almost ready and everything works fine. I was using free account to test my code. The question is: which account plan should we use in production? The only thing our app depends on is API Calls per month, we don't need a big storage (because users will use their own accounts for export) or some other features. Free account's characteristics were perfect for our case.
It sounds like you're referring to what kind of Dropbox account should "own" the API app itself, is that correct? (The account that "owns" the app is the one that can access the app's information and configuration page on the App Console.)
The particular kind of account that owns the app doesn't really matter. Any kind of Dropbox account can own any kind of Dropbox API app. That won't affect the app's functionality. The functionality instead depends on the end-user's Dropbox account. (For example, any kind of account can connect to a "Dropbox API" app, whereas only Business accounts can connect to a "Dropbox Business API" app.)