Prefered form of navigation with persistent BottomNavigationBar - flutter

Question

I am making an app that has a persistent BottomNavigationBar. Depending on user != null the user gets into the LoginScreen or HomeScreen
There are two ways to get this done by routing:
First approach: include LoginScreen inside the nested Navigator from the MainScaffold
the mainScaffold the user gets redirected from, will have a body that has its own Navigator class inside that body.
App
class AppName extends StatelessWidget {
#override
Widget build(BuildContext context) {
return MaterialApp(
home: MainScaffold(),
);
}
}
RouteGenerator
class RouteGenerator {
static Route<dynamic> generateRoute(RouteSettings settings) {
final args = settings.arguments;
dynamic builder;
switch (settings.name) {
case '/':
builder = LoginScreen();
break;
case '/mainScaffold':
builder = MainScaffoldBody();
break;
case '/mainScaffold/page2':
builder = (BuildContext context) => Page2();
break;
...
default:
return _errorRoute();
}
return PageRouteBuilder(
...
pageBuilder: (BuildContext context, _animation, __animation) => builder,
...
);
}
MainScaffold
class MainScaffold extends StatelessWidget {
...
#override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBarSelector(),
body: Navigator(
key: _navigatorKey,
initialRoute: '/mainScaffold/home',
onGenerateRoute: RouteGenerator.generateRoute
},
),
bottomNavigationBar: CustomBottomNavigationBar(controller: _controller),
);
}
}
Alternative: don't include LoginScreen inside the nested Navigator from the MainScaffold but seperate it
The alternative approach would be to have MainScaffold as initialRoute and LoginScreen inside the bodyof the MainScaffold.
If I want the BottomNavigation to dissapear on for example LoginScreen, I could simply toggle the sized/visibility of that bar. The RouteGenerator would look like such.
App
class AppName extends StatelessWidget {
#override
Widget build(BuildContext context) {
return MaterialApp(
initialRoute: '/',
onGenerateRoute: RouteGenerator.generateRoute, // this static creates possibility of using parameters
);
}
}
RouteGenerator
class RouteGenerator {
static Route<dynamic> generateRoute(RouteSettings settings) {
final args = settings.arguments;
dynamic builder;
switch (settings.name) {
case '/':
builder = MainScaffold();
break;
case '/login':
builder = LoginScreen();
break;
case '/mainScaffold/home':
builder = HomeScreenArguments();
break;
...
default:
return _errorRoute();
}
return PageRouteBuilder(
...
pageBuilder: (BuildContext context, _animation, __animation) => builder,
...
);
}
So what is the best approach here:
LoginScreen is part of the nested Navigator from MainScaffold
LoginScreen is not part of the nested Navigator from MainScaffold