[arbok]

There are so many dog/cat designs because they're relatable.
You feel more attached to a dog or cat than you do a Pokeball or an Ice cream.
Good example is how I have always loved Growlithe. Always. From the moment I saw the puppy I knew I wanted one and even now I have just finished White 2 with an Arcanine on my team. Another of my favorites I have finished White 2 with is Magnezone. I spent years not caring about the Magnemite line one bit. It was only when I caught a Magnemite on a whim and raised it did I start to care about it, only when it won me a great many battles did I think it was cool.
It's because you can relate more with a puppy than a magnet.