Help users focus the most obvious action

This module is a game-changer for IEF, thanks a lot! We're getting really close to help users understand what they're expected to do with inline entity forms.

Last tidbit in terms of user experience: In case both add existing and create new are configured, help focusing the most obvious option.

My idea would be to present the two forms in horizontal tabs if the viewport is wide enough (I might be biased here, looking at a form with horizontal tabs field groups present).