Day 4: Okay, this is a hard one.
For the side-couple, that overshadowed the main couple the most to me, I would pick Leon and Pob from "Don`t say no". They had a cute storyline and were great together on screen. I`m really looking forward to their spinoff-show (though I`m pretty sure MAME will find a way to blow it).
My favorite side couple in general, however, would be Jack and Zhao Li An from "History 3: Trapped". They had great chemistry and are one of the main reasons why I`ve rewatched the show so many times.
Honorable mention: "Cutie Pie"`s Syn and Nuea are kinda taking over my heart right now. (even though they`re technically not a couple yet)