My, my. Hopefully this won’t qualify me as a nerd. If I must choose only one it’ll be Espeon. If I can choose six they’ll be:
Blissey, Jynx, Lopunny, Milotic, Lilligant, and Espeon. It’s my rule to only accept female pokemon in my team (except genderless pokemon), and it kills me having to soft-reset every now and then just so I can get a female starter.
Additionally, I hate the idea of mega evolution as the ones that get it are only stereotypically popular pokemon that are already strong to begin with, leaving less popular/weak pokemon to become less beneficial to be used.