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.