So, here's the quick version, the other one is huge, and you can see it if you want by clicking on the edited button.
Most number of highest Stats: Togekiss
Best Defenses: Gyarados
Best Movepool: Tie Between Altaria, and Gyarados(Very Close Second/Tie, Staraptor)
Best Abilities: Gyarados/Staraptor(they both have the same one.)
Easiest to Evolve to final Stage: Staraptor
HOWEVER, A Few Notes,
1. In-game, defenses don't matter a lot, it's all about the offense, and who can do more damage faster, and Staraptor's top stats are in Attack and Speed, so that changes things.
2. Staraptor gains most of it's super good moves from Level Up, the easiest form of move learning, making it even more convienient and good to have.
So, the winner, is Staraptor, as it has good stats, and great movepool for In-Game, and is more convenient to get and evolve. Also, Gyarados can't learn Fly, Staraptor can, so choose Staraptor.
Final Answer: STARAPTOR
Source: Lots of cross refrencing between the pages of this site.