Well, it depends. I would choose Snorlax if the size of the pokemon is pretty big when it follows you.
If not, I'll choose Togekiss, my Favourite Pokemon
What I mean by it depends is, see how when you walk in the Amity Square in DPP your Infernape, Empoleon or Torterra, their real size should be way bigger but in the Amity Square, it size is made to suit your player more so that it is more negotiable when you are turning corners.