Let me answer this real quick:

As shallow as it sounds, it's a combination of artistic skill, what's currently trending, and how well the OC's fashion is put together.

The Viser League is MAJOR example of this, because I'm enamored with a lot of the trainer OCs portrayed during the first and second zines. If I had to choice my favorites, it's easily Helly's OC - White, Doon's OC - Tristan, Hour's OC - Hayden, Sachis OC - Shane, Mori's OC - Saigo, Ryai's OC - Michael (MOST DEFINITELY XD), Amai's OC - Maya, Glitchy's OC - Glitch, and soooooo many others worth naming but can't possibly fit here.

Now, if I throw in potential friendship compatability with my main man, Elio, then the likability will soar through the roof. It's currently why I'm so enamored with Lindow and Ruth because irl - they're the people Elio's most likely to befriend and grow close to.