The correct answer is number of words.
When you are analyzing a poem, you are trying to find its meaning, or rather, the theme that the poem is presenting. There are many ways to do this, but the most common one is to interpret the literary devices the author used, the literal and figurative meaning of his/her words, and the structure of the poem itself.
Whether the poet used just a few or a lot of words has no particular impact on the theme of that particular poem.
