Question

Is it better practice to have one root view controller that handles transitions between child view controllers, or switch root view controllers when necessary?

And can we have custom animations with presentViewController:?

Answer 1

which means I can’t use [presentViewController:animated:]

This is incorrect. You can do something like the following:

NewTestViewController *newTestController = [[NewTestViewController alloc] initForPhone];

newTestController.view.frame = CGRectMake(0, self.view.frame.size.height, self.view.frame.size.width, self.view.frame.size.height);
[self.view addSubview:newTestController.view];

[UIView animateWithDuration:0.3 animations:^(void){
    newTestController.view.frame = CGRectMake(0, 0, self.view.frame.size.width, self.view.frame.size.height);
} completion:^(BOOL worked) {
    [newTestController.view removeFromSuperview];
    [self presentViewController:newTestController animated:NO completion:nil];
}];