Best practice e2e testing

We are building an automation suite for our mobile app.

During the brainstorming we did , one issue has pumped up , what is the best practice to implement the tests ? Is the right way will be while each test (story file which contains several scenarios) initial the application from scratch (we are using iOS simulator / GenyMotion) - restart the device , which means each story file we perform new login , or maybe we need to assure that each new story file starts from some landing page ? Then in that case , the login / logout being performed only once ...

WDYT ?

Thanks