I don't go by favorites, but not by power either. I like to use all the Pokemon, and explore their individual abilities. I don't like the idea of dismissing a Pokemon just because of its appearance... When making teams, I do look for a Pokemon with the right moves/stats/ability for the job, but that's because I don't really have favorites. I do dislike using the same Pokemon too much though, which is why I find myself trying to utilize Pokemon in the lower tiers often. There's nothing that irks me more than "OU spam".