I almost always choose Grass or Fire starters. Before getting diamond, I thought to myself, "whichever one I get, I'm not getting the stupid monkey." Well, I ended up getting the stupid monkey 'cause I wanted Floatzel and either Pachirisu or Shinx (went with Shinx). It ended up not being so bad, I like Monferno but Infernape is not one of my favorites. In Platinum, I picked piplup because I hadn't gotten one yet.
For HG, I picked tododile, but immediately ditched it for Horsea (my plan all along). The idea for my run was that after beating each gym, I would gain a new pokemon on my team that matched the gym's type. So, after beating the dragon gym, I finally evolved my Seadra into Kingdra. It was pretty awesome. If I hadn't done that, I probably would've picked Cyndaquil (my starter back when I played Crystal version) or Chikorita for a change of pace (I have some sort of grudge against Tododile I guess).