Typhlosion would have to be my absolute favorite starter.
First off, it's got pretty good base stats. It has a pretty useful Sp.Atk at 109, though its base Attack at 84 can make for a decent mixed battler. It makes up for its low base 78 Defense with a decent base Speed of 100, allowing it to move faster than most physical Water-, Ground-, and/or Rock-types.
Second, its movepool is excellent for a mixed attacker. It's got access to a lot of great Fire-type moves, both Physical and Special. It also has Flare Blitz and Reversal as egg moves. Its TM moveset is broad enough to cover two out of three of its weaknesses, making it a pretty versatile competitive 'Mon.
Third, its design is appealing. The steely blue on its back does well to contrast the flames around its neck, as well as the nice cream color on its legs and undersides.
Finally, its Pokedex entries make it pretty clear that this Pokemon loves to use fire and heat to express itself.
There are so many entries that I can't list them all, though. I can't really decide which one(s) to include here, either, so you can read them on Bulbapedia if you're interested:
http://bulbapedia.bulbagarden.net/wiki/T..._(Pokémon)
Mine tend to look like this:
Typhlosion @ Wide Lens
Flash Fire
Hasty or Timid
252 Sp.Atk/4 Atk or HP/252 Speed
- Focus Blast or Reversal
- Wild Charge
- Blast Burn, Lava Plume, Explosion, Fire Blast, or Flare Blitz
- Sunny Day or Hyper Beam