I know just about everything there is about Sharks, so I would pick Garchomp, because he is cool looking, and more versatile than you guys think..
With Tyranitar on your team or anything with Sand Storm, his Evasion helps out greatly, not to mention that he has STAB Earthquake, and is a counter to Tyranitar, which is greatly abused.
If most of you that are choosing other Dragons are just choosing based on which of those 3 Dragons can win in a battle against each other, you are missing many other key factors..
Garchomp has excellent stats, having good defenses to back up attack that is not even 10 points away from Salamence.. and being the fastest Dragon wins me over, because I believe that Dragons are supposed to be fast already...