My advice is to take your teacher's question at face value. Simply read each play's opening scene for pure enjoyment, taking note of what you like or dislike, what you understand or find confusing. When finished, simply rank your favorites 1-4. If you can clearly and thoroughly explain to your teacher which opening you prefer (and why) you will have addressed the assignment's main purpose. Some things to look for...
- Notice how Shakespeare often opens his plays by dropping his audience into the middle of an ongoing conversation (true of all four of these plays). While initially confusing for the audience, this technique works on two levels. First, forced to play "catch up", the audience begins to predict where things are headed; this motivates us to press on (if we are intelligent, diligent scholars) and gets us thinking about character, plot, and theme. Meanwhile, the playwright is able to provide us with necessary preliminary information (think "exposition" from the well-worn plot diagram). By the time the main action ensues, the audience is interested, on the same page with the author, and ready to apprehend the play's key conflicts.
- Shakespeare often opens his plays with minor characters and rarely (if ever) the protagonist. This is true of three of the four plays you list, and is almost true of the fourth: Othello opens with a conversation between Roderigo (a brilliantly utilized minor character) and Iago, the play's villainous antagonist. In fact, Iago is arguably the play's main character; certainly he is more complex than the title character, and he is given more lines and more stage time than is Othello.
Hope this is enough to get you started. Good luck. :)