This is a tough one. In terms of sheer "cool" factor, the only one of the twelve fully evolved starters that turns me off is Meganium, which bodes badly for the Johto starters, let alone the fact that none of them gain a secondary typing when fully evolved.
Kanto's has the kind of charm that comes with nostalgia. They're classics that nobody can hate, but likewise, none of them really stand out as unique in terms of movepool and stats.
Sinnoh's, while I initially despised Empoleon's and Infernape's designs, They've grown on me, particularly because of Empoleon's uniqueness and Infernape's stats and movepools. This doesn't change the fact that torterra is the only one of them that actually has a cool-looking design. :<
...Which lead's me to the Hoenn starters. A large jungleborne lizard, a fierce fighting chicken, and an angry-looking amphibian. All three of them pass the badassery test. Whatsmore, they're all unique...Sceptile being the fastest grass-type pokemon in Hoenn, Blaziken being the first fire-type to reliably counter their traditional weakness to Rock-type pokemon, and Swampert generally being able to counter everything the in-game gyms and E4 throw at him.
I'd say the winner here is clearly the hoenn starters. :P
