I enjoy the Marriage of Convenience trope the most, because I'm interested in how two people negotiate a marriage, given their myriad backgrounds, experiences, hopes, disappointments, and dreams. It's not "why" two people get together, so much as "how" two people stay together in a relationship that has mutual affection, respect, consideration, dedication, and support.
I also enjoy the Friends to Lovers trope, and again, my interest here devolves to interest in how they negotiate a marriage given their mutual history.
I like to see characters behave with maturity, dignity, integrity, and empathy. And I like seeing their love gradually unfold on the page.
I enjoy reading about characters who do "work," who have passions and interests that they assiduously pursue in the story, and who have lives beyond simply malingering at the other's feet. Work makes people interesting.