WoWDB

Not merely cute, but a surprisingly powerful Battle Pet. One of its many variable stat types ("Natures" to coin a phrase) is a heavy Power build: 149/14/10 at level 1. That stat build's low Speed is offset by the Flying Passive (increases Speed by 50% while it remains above 50% HP). Also, since the pet is only 40g (assuming you have Exalted), you can just buy several of them until you get the stat setup that you like and cage and sell the rest.

Additionally, the Nether Ray Fry's moveset is pretty amazing. It has excellent 'type coverage'. All six of its abilities are what I'd call "basic attacks" (they have no real secondary effects and no cooldowns), and they are ALL different types: one Magic, one Beast, one Elemental, one Undead, one Flying, and one Dragonkin. This makes it extremely valuable when facing many different Pet Tamers, since you know their lineup in advance (or at least you do if you look it up or try to fight them and forfeit/fail) and can swap in the moves for the Nether Ray Fry that you need.

The only real issue with the Nether Ray Fry is that he isn't a team player. His moves have little or no synergy with the rest of the team, so you may not want him a pure level 25 "optimal" setup. However, I still think the Nether Ray Fry is awesome for leveling and defeating pre-Pandaria pet tamers.

Powerful, Versatile, and most importantly, Cute.