For me, I really enjoy good chemistry between the couple! It's really hard for me to not ship couples who were buddies before they started dating, haha. Also, I like it when they still have the friend like bond, even when dating. I also am a sucker for romances when the couple starts out as a couple and we can see their progress! Though, I also do enjoy it when they get together after a while.
Rivals turned friends is good too! Maybe even "hate" to love. But, that takes time. So, if the author or artist rush it, it feel blegh for me. Like, "okay they hate each other-- wAIT WAIT WAIT WHY ARE THEY KISSING-" it just baffles me because hate is a strong emotion. Unless, of course, they pretend to "hate" each other solely to hide their feelings but I rarely see this TTvTT
I also don't mind reverse harems or harems (okay some are really painful but-) because when the heroine has spunk and character, it turns our really interesting, you know? Like, their interactions between the many different characters. It's also a mystery to find out who they end up with! And it's a total good bonus when they actually do end up with someone. This goes for love triangles too <:
Also, the soulmate AU is pretty good too and I'm weak to that.
People dating out of the blue on an arranged marriage and such is amusing to see, too. Character development is good!