My two choices are Dr. Faustus and Waiting for Godot.
Dr. Faustus is the typical tragic hero and it prompts me to analyze a lot when I read a story about a man who has all the capabilities to make something greater than he already is, and instead uses that energy completely diversely, ending up basically destroying himself out of his own arrogance.
Waiting for Godot is another of my favorites due to being absurdist and given that my personal choice for absurdism has always dominated my literature choices.
I think that I am probably more partial to Beckett's work. This is not to say that the other three are not invaluable in their own essences, but I have always had a liking to Beckett. It is a challenging work to read through, but its lessons are priceless. The idea of "Waiting" for an external force to provide some answers, something in terms of absolution, or some configuration of resolution is an element that strikes at the heart of what it means to be human. To "wait" is something that seems to undercut not only much of consciousness, but all of literature as well. The manner in which Beckett brings this condition out in his characters and in the reader is something that is supremely powerful and meaningful.
I see I'm a latecomer to your question; you've already quite a string of answers. Well, I'll just add one more layer to it for fun. If I have one choice from these plays as one that I like, it would be Dr. Faustus. Marlowe used Dr. Faustus to explore the consequences of the complex choice between the ultimate pursuit--in Faustus' case, perfect knowledge--and human integrity.
Faustus discovered that the promises of ultimate attainment and unwavering success eventually come face-to-face with the universal realities of what the Greeks called the Fates and Christians call powers and principalities and Faustus called Mephistopheles. The end knowledge--the ultimate knowledge--is that humankind is bound, hedged in, limited by the ultimate nature of the baryonic universe: all universal matter tends to decay and thus cannot limitlessly move forward.
Newton proved that a circle is a straight line bent into an adjacent direction by an incoming impetus force. With each consecutive bump, energy has the potential of being spent at a rate greater than that at which new energy is gained from the bump, decayed so that eventually the circle has the potential to grow smaller and smaller. This is a neat metaphor for the limitations inherent in the nature of the baryonic universe (maybe dark matter and dark energy don't decay...) that is mentioned above.
I'm not sure an editor can help you with this question. I wouldn't complicate the issue. If you've read all four, choose one and tell what you like about it. There are a seemingly unlimited number of things to like about any of these works. You have tragedy, comedy, absurdity, etc., to choose from. You have works from different literary periods by writers from different countries. You have plenty to choose from.
The reader-response question--what do you like about the work--is so vague you can pretty much write whatever you want. I would simply write what you like, period.
I love Hamlet, by William Shakespeare! There are so many different interpretations and levels to this text, and I think it's really interesting to explore each one. First, one could simply concentrate on the character of Hamlet as he grapples with depression and the fruitlessness of life. Secondly, as a revenge play, I find this tragedy to be extremely interesting. Hamlet is a man obsessed with avenging his father's death, and he will not rest until he is able to do so. I've never read A Midsummer Night's Dream, and Dr. Faustus wasn't that appealing to me, either. Also, I found Waiting for Godot to be incredibly annoying and dull, and I just didn't "get it", even though it's considered to be existentialism at its best.