Which one to choose, custom app or public app?

[Shine18pk]

I have a client, who has 3 stores, ( 1 global, 1 for eu and 1 for au). Now, i am going to create an app for her which will be going to install on all 3 stores ( this is requirement because data will be synced between stores). 
I'm having problem choosing custom app or public app. Since custom app can only be installed on one store, and public app can only be installed on merchant stores, when approved. 

Currently i'm building the app in draft mode. 
Can anyone guide me what to do here?

[pascallaliberte]

I'm in the same boat. One app, one client, two stores.

I'm wondering whether I can make the following setup work with the custom app option:

• One codebase
• Two directories locally, one for each instance of the app in my Shopify Partners account, where I'll call the apps differently: "App Name (Store A)" and "App Name (Store B)".

Or if going for the public-but-unlisted option, this setup:

• One codebase
• The client creates a Partners account that I join as a contributor, and the client publishes the app as public-but-unlisted.

I'm leaning toward the public-but-unlisted option.

[pascallaliberte]

But then maybe there's this other option: first-custom-then-public.

• I can start with a custom app,
• and eventually use the same code to re-create it as a public-but-unlisted app when comes time to install it on a second store.