I won't vote, since there's no correct answer.
The best thing is not either one of them, but a combination of both.
Userfriendly interface and gui for the standard enduser and on the other side a lot of api and libraries for developers.
And if you have that case & developers, who are actually using existing APIs for userfriendly guis, you have a working lifecycle.
Users are downloading apps, developers are uploading apps & the amount of apps is growing, growing and, correct, growing.