My vote came down to either Rattata or Zigzagoon. Patrat is decent, but Lillipup is easily better early on in BW. Sentret never really seemed to be useful to me in gen 2. Bidoof works well as a HM slave, but that is about it. I voted for Zigzagoon because of its pickup ability early on and a Linoone with headbutt is great. I also like Rattata, but the tiebreaker went to the ability.