In terms of what Pokemon I would like to be, I would probably most likely choose Mew, just since Mew is a powerful Psychic Pokemon, can fly around, has unique abilities, is just plain cute, and Mew seems to be a very happy-go-lucky type.
In regards to which Pokemon I think I am most like though, I guess it would be (based on an assumption I can make from my own knowledge of all the Pokemon) Pidgeot, because ever since I was a small child, I always wanted to fly (and I mean on my own). So, I used to collect bird feathers, thinking if I got enough together, I'd be able to fly with them. As I grew older, eventually I learned that was silly and stopped. But even working at a dog kennel for my first job back when I was 16, I used to "communicate" with the birds there, and after having worked there for so long, I even developed a relationship with one of the red-winged blackbirds who would fly around me, landing next to me, and who would even let me get within just a couple of feet from him. I feel like I have a connection to birds, but more than that, I have always been a free-spirited person with big dreams and a fairly-sharp mind. Being able to fly at Mach-2 speeds wouldn't be bad either!