I'm picking a legendary because really, I can just catch the normal pokémon.
Ho-Oh: I'd look like a boss flying on it.
I'd want a Poliwag.
Farfetch'd. 'Nuff said.
It'd have to be a Gible (--> Garchomp) a Bagon (--> Salamence) or an Axew (--> Haxorus) for the sheer awesomeness.
You ever see that episode of Pokemon Chronicles where the guy with a Chikorita on his shoulder battled his Salamence against a Moltres (iirc)?
That would be my kind of pokemon adventure, testing my skills against legendary pokemon, going where my pokemon wanted to train. I have the idea that my dragons would want to go somewhere cold to train against their weaknesses. They'd take a beating but at that point they'd probably learn Outrage xD and would be stronger for the experience, Sayian-levelling style :)
oh and incoming epic haxorus picture
sig courtesy of blue dragon http://bmgf.bulbagarden.net/f379/blue-dragons-art-shop-122227/
Pearl friend code: 1334 8992 8416
White friend code: 1334 7742 9693
I'd go the old boring way and chose a normal starter, in my case Tepig, mostly because it evolves into Emboar, my favourite Pokémon. Emboar itself is the kind of Pokémon I can see as being vital in a Pokémon journey, I always saw him/her as a kind of stalwart protector which I would require if I wanted to survive in the wild, with Pokémon everywhere. Although, as a second choice, I wouldn't mind Starly, a Staraptor could turn out to be useful for travelling and is still pretty strong.
Gible, Eevee, Absol, or Houndour would be my choices. Gible eventually becomes Garchomp. Eevee has the versatility of several evolution paths (I'd choose either Espeon or Umbreon). Absol's Super Luck ability and moves like Psycho Cut make it deadly. Houndour evolves into my favorite Pokemon, Houndoom.
Charmander, I'm obsessed with Charmander. Since I was a little kid I wanted a pet Charmander.
A Ditto. Think of the breeding possibilities! It could also turn into just about anything, so I wouldn't get bored of just one pokemon. Battle ability does become a problem though...