I like to choose based on typing, I love psychic type and they have incredible suporting movepools most of the time (something i love) I like to lay a little defensively (good defensive stats always help) and using a lot of tricks so they fit right there, screens, reliable recovery, magic coat, all moves I love and most psyquics i have have them all (or will have them), their supporting capabilities and nice abilities is the second thing I choose, but for example something like scrafty, even if it fits my criteria is too ugly to choose, a good typing helps too, but most of the time i like someone with a great movepool and that actually looks good (togetic, dragonite, roserade), i'm against gengar since even if it's one of the best pokemons in every way is to mean for me, other ghost types are cool, but mostly i go for awesome supporting movepools and a way to not die (that's why most of my team is psyquic (future), normal and dragon (cause they are cool)).
Trolling is definetly a part of me so i'll probablyget a hoppip sometime or something like it, but playing tricks is the way i like to battle, still i think I need more water type, but the only screener with recovery is staryu, milotic will be mine (since i've love her since she was out), and something cute, Vaporeon and Slowbro probably
Still, i'm waiting for a tournament that gives away Celebi, i will definetly do everything to get him (i really love the pixies, Celebi, Jirachi and Mew)