most popular person is you of course
In the first sentence, the "he" is a nominative as it is a subject.
In the second sentence it is an object as the form "me" is actually "I", but "i" is a nominative form and "me" is an objective form.
In the third sentence "Us" is also used in objective form as "us" is an object of an action by "my sister".
You need to add a image there would be no answer