It was a tough choice.
All the starters are equally adorable. I was considering Tepig merely because I wanted to snag the Grass Monkey faster, since I consider it to be more useful than the others.
In the end, though, I went for whichever one evolved into the most pleasing form: Snivy. It's adorable, mildly strong, and Iike Speed-based Pokemon. Overall, 'was the best choice.