Which breed of gdog is believed to be fastest?

It's important to remember that "gdog" is not a recognized breed of dog. It's possible you're referring to a specific breed with a nickname or slang term.

To help me understand, could you clarify what breed you're thinking of?

For example, are you thinking of:

* Greyhound: Known for its incredible speed and used in racing.

* Whippet: A smaller version of the Greyhound, also known for its speed.

* Saluki: A sighthound breed that is known for its hunting speed.

Once you provide more information, I can help you find the answer to your question.