Looking over my characters rank 10+ I have: Ambra, ISIC, Benedict, Phoebe, Reyna, Kleese and Shayne & Aurox.
Of those I use the default skin on: ISIC and Kleese.
I use the white faction pack skin on Ambra, Shayne & Aurox because I really like the white skin look.
I use the mastery skin on Phoebe, because I find the purple and black matches her personality well.
For Reyna I use a random faction pack skin (Rapscallion), but there really isn’t a skin I like that much for her.
And for Benedict I use gold eagle, because covering himself in Gold is definetly something Benedict would do. Though I am very tempted to get the Murri-Caw skin.
I personally don’t mind the default skin being the best looking skin, as long as the others aren’t objectively worse. And that has been the case with most MOBA’s I have played, where the default skin is usually a good bet unless there is a specific look you are going for.