ASP.Net MVC - Conditional Unauthorized Redirects

1- You could inherint from the [AuthorizeAttribute] and customize the implementation to route to the desired Unauthorized page.

See the selected awnser is this question: Redirecting unauthorized controller in ASP.NET MVC

2- If your are loading partials from an ajax call, (ie., $.Get(url) or $("#somediv").Load(url)), make sure the actions called by url are properly decorated with your custom [AuthorizeAttribute].

Otherwise, you will need some logic in your razor views to check if the user is authenticated. Something along the lines of

  @if (User.Identity.IsAuthenticated)
  {
      // Normal case
  }
  else
  {
      @Html.Partial("Login")
  }

Where your Login partial would show the desired login view.

Update

You could implement 2 different attributes, one for each scenario.

[AttributeUsage( AttributeTargets.Class | AttributeTargets.Method, Inherited = true, AllowMultiple = false )]
public class IsUserAdminAttribute : CustomAuthorizedBaseAttribute
{
    // Custom logic to redirect to admin logon partial/view
    ...
}

[AttributeUsage( AttributeTargets.Class | AttributeTargets.Method, Inherited = true, AllowMultiple = false )]
public class IsAuthenticatedAttribute : CustomAuthorizedBaseAttribute
{
    // Custom logic to redirect to basic/comment logon partial/view
    ...
}

[AttributeUsage( AttributeTargets.Class | AttributeTargets.Method, Inherited = true, AllowMultiple = false )]
public abstract class CustomAuthorizedBaseAttribute : AuthorizeAttirbute
{
    // Shared custom logic implementation
    ...
}

And you could use one or the other, depending on the scenario, to decorate your controller actions.