I don't necessarily refuse playing high tiers out of principle, but I don't go to them because:
A. I don't like their fighting styles
and
B. I have slight aversion to playing popular characters in fighting games (maybe I'm a hipster).
What usually guides my choice is what characters I like as a fan. I main
![Shulk :4shulk: :4shulk:](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)
because of my love for Xenoblade, a game I've beaten twice with hundreds of hours of playtime.
I also like
![Ganondorf :4ganondorf: :4ganondorf:](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)
because I grew up on the Zelda series and I've liked him in Smash since Melee when I first felt that wonderful feeling of surprise at seeing him appear in the game.
I play
![Samus :4samus: :4samus:](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)
from time to time because I also am a big Metroid fan and have played every game in the series. I'm not a big fan of camping though, so I probably don't use her arm cannon as much as I should.
And lastly, I have been attempting to pick
![Bayonetta :4bayonetta2: :4bayonetta2:](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)
up because I love the games and I never thought I'd see her in Smash. It's a shame that so many people have hard feelings about her playstyle, so I only sparingly use her.