Well the first pokemon I knew about (happy meal toy) was Magnemite, and I like to believe in destiny, so he would be my first pokemon. Coincidentally, I ended up with every Magneton card except Lt. Surge's up until I stopped buying pokemon cards. Plus Magnemite is just pretty cool and I might have picked him anyway.
I would start out my journey with a little Chingling holding an Everstone I gave it.
I'm really torn between Tepig or Charmander! Tepig because he's my favorite starter and Gen 5 is my favorite. But the first game I ever played was Blue and Charmander was the first Pokemon I ever trained...and eventually he'll be a Charizard <3 If I decided to start with a Tepig, I'd make him stay a Tepig forever.