The correct answer is 3 (the relative merits of French and English theatre) because one of the key debates in John Dryden's "An Essay on Dramatic Poesy" revolves around a comparison between French and English dramatic traditions.
In the essay, Dryden presents a dialogue among four speakers: Eugenius, Crites, Lisideius, and Neander, each representing different perspectives on theatre. The discussion prominently contrasts French and English drama, focusing on the strengths and weaknesses of each. For example, the French style is praised for its adherence to classical rules like the unities of time, place, and action, while the English drama is appreciated for its greater creativity, variety, and emotional depth.
Thus, the main debate centers on the relative merits of French and English theatre, making answer 3 correct. The other options (1, 2, and 4) do not align with the core thematic focus of the essay.