What do you think are the strongest species in the Alpha Quadrant?
Some species to consider besides human, Vulcan, Klingon, and Romulan are the Andorians, the Betazoids, etc.
You could also classify them by political entity, such as:
2. Klingon Empire
3. Romulan Empire
You could also count the Borg as an AQ species even though they were originally from elsewhere.