I would strongly suggest selecting another dramatic monologue by Robert Browning. He certainly is the master of dramatic monologues, and it is clear that the various aspects of "Porphyria's Lover" are evident in his other poetry. Why not select a poem such as "My Last Duchess"? I have included the link to the enotes section on this poem below, along with the section for "Porphyria's Lover." Both of these poems are dramatic monologues related by somebody who is definitely not a reliable narrator. Although the situations and contexts are different, both poems revolve around the death of somebody important to the speaker and they would both give you ample scope to compare and contrast Browning's skill in creating dramatic monologues. In particular, you will want to pay attention to the vague way in which the death of both women in these poems is refered to and what that in turn reveals about the narrators of these poems. Good luck! I am sure this will be an interesting comparison.