The two murders were both committed out of a sort of revenge; Montresor because of insult received, Emily because of jilted affections. Montresor just wanted straight-up, merciless revenge though, whereas Emily desired love forever (real or rotting). :)
The title should creatively reflect the main point of your essay. Will you conclude that the only commonality was a leaning towards mental instabliity? If so, then the title could be "Insanity: A Symptom of Murder". If there are more commonalities to discuss, in the form of revenge, it could be "Revenge: A Symptom of Insanity". I would make a compare/contrast list, see what you come up with for a main point, and get your title from that. I hope this helped some!
I think your essay needs to focus on the two central characters and the way that they are both presented as deranged and somewhat eccentric (to put it mildly). #2 is also right in insisting that revenge is a theme that needs to be discussed - both Montresor and Miss Emily kill out of revenge, but only because of their own slightly unbalanced personalities.
Comparison/Contrast Essay: "A Cask of Amontillado" and "A Rose for Emily"
What would be a good title for an essay comparing and contrasting the motives and mental states of Emily and Montresor?
Usually a title can be found in the wording of the assignment.If you are supposed to focus on the motives and the mental conditions of the two characters, you can include these terms/ideas in your title. For instance:
Miss Emily and Montresor: Motives and Madness
This one has a nice ring to it since it uses alliteration of the "M" sound. Also, it is an open title because it doesn't pin you down to either comparison or contrast. It would cover both.
I agree with the first response but I would also consider that both Amontillado and roses are red. So you could go with some kind of alliterative title like: "Red Revenge" or "Case of the Red Revenge" or even a play on words like "Read Revenge" or even "Cracked-up Killers". You know better than we do what your English teacher will like better, something more traditional or something a little more creative. Good luck with your paper!
What about "Entombed by the Mind" since both Emily's and Montesor's perceptions were buried in the past: Emily was lost to the mindset of the Old South while Montesor had his thinking walled in by his insistence that he suffered "a thousand injuries" in the past and must have revenge.
"An Eye for an Eye"
Both Emily and Montresor felt they had been wronged by their victims.
In a "Cask of Amontillado", the reader never learns how Montresor was mistreated to the point of wanting to commit murder. In a Rose for Emily, she didn't want to be abandoned or rejected.
Both Emily and Montresor allow vanity and delusional thoughts to take over their sense of reality.