Like many others, Charmander was my first pick. It had that mixture of being cute and looking strong at the same time, and I was sure it was the best choice for me. Well, the first few hours of the game tried hard to convince that it wasn't, because I had a really tough time getting past Brock and Misty, especially since I had no knowledge of the mechanics or anything back then :p And while it eventually grew to be a strong fighter, I didn't use one for a long time after, just because of how tough the start proved to be for little 3 year old me :[
My first choice nowadays is, and probably will always be Bulbasaur. Additionally to really liking it design-wise (well, mainly the first two stages. I don't like Venusaur's design quite as much), it makes the first part of the game so much easier and fast to get through than with Charmander (even though its moveset has been updated to accomodate for the first gym), and the lazy side of me really likes that ;D