Used to highlight the specific feature that makes one option clearly different from or better than another.
“Both plans are similar, but what really sets it apart is the free cancellation policy.”
“What really sets it apart is the warranty — it covers repairs for a full three years.”
This phrase works well in Task 5 when your two options are fairly similar overall, since it lets you zoom in on the one distinguishing feature that tips the decision. Use it after briefly acknowledging both options are decent, to show balanced, thoughtful reasoning before making your final point.
Synonyms: what makes it stand out is, the key difference is, what distinguishes it is