I don't have a preference, I pick the starter based on whether I liked the Pokemon or not (by it's looks - and the animal its based on)
Gen 1 - Kanto - Squirtle, I didn't rally like any of the 3, but when I had to pick most of the time I went with Squirtle.
Gen 2 - Johto - Cyndaquil, it's the only one I liked in the second generation, mainly since when it evolves it becomes partial weasel, they are my #1 favorite animals in real life.
Gen 3 - Hoenn - Mudkip, not really a fan of any of the 3 starters this gen (by design didn't like any of them, Torchic was the worst), so if I had to pick one it would be Mudkip
Gen 4 - Sinnoh - Chimchar, slowly started to like both Monferno & Infernape (still dislike Chimchar's design a bit).
Gen 5 - Unova - Oshawott, #1 reason is still my most favorite of all starters to be created, a cute Sea Otter!! I love mustelids - otters are aquatic mustelids, it's all the reason I need for Oshy to be my favorite starter, Dewott overall is my #6 favorite Pokemon of them all.
Gen 6 - Kalos - Fennekin, second favorite of all starters to be created, Braixen is my #11 favorite Pokemon. Main reason I like it because it's based on cute foxes.
Water - 3
Grass - 0
Fire - 3