A comedy lol seriously - it'll give you insight on the person's humor, how they analyze what they see and hear, etc.
If you're already in a relationship, then I would come to an agreement together on the kin dof movie - I would say it depends on how both of you feel that evening.
Relaxed? Love Story.
On top of the world? Action
General good mood? Comedy
I think horrors are always an awful choice so...
Are you more business oriented? Spiritual? It depends on so many things, no one can really answer this but the two of you. Still, I hope I helped somehow.
God bless you.