Based on what is known about the various quadrants' species, rank them from most powerful/threatening to least as of the end of Nemesis, assuming each quadrant was to unite (keep in mind that the Klingon and Romulan Star Empires reside mainly in the Beta Quadrant, don't they?). For those species whose territories expand beyond Quadrant boundaries, guesstimate influence in each (ex: X% of Talaxian Empire in Delta Quadrant, Y% of Talaxian Empire in Gamma Quadrant).
My rankings (until influenced by other posters):
Delta
Gamma
Beta
Alpha
My rankings (until influenced by other posters):
Delta
Gamma
Beta
Alpha