I am really wondering what the rarest pet is. Because I am a total pet collector and need your help! Since I was given (by my friend) a Level 100 myth account, the only thing I can actually do is help people and collect pets. So I want to know badly what is the rarest/most powerful pet.
The rarest pet is the one you're having the hardest time getting. Some might say a Fragmented Dragon, but there are some people who have dozens of them.
I've only ever seen one person that has a Firebat so to me that seems rare, but I could probably find people who would say they've seen more Firebats than they can shake a stick at.
For the most powerful, again, it's a personal thing. What I think is a powerful pet might not be powerful to someone else. Similarly what they think is powerful might not be powerful to me.
Typically first generation pets aren't going to be powerful in the way I perceive your inquiry to imply. Power comes from hatching and training. If you hatch and train with the right pets, you could wind up with a Brown Dragon that becomes the most powerful pet you've ever had.