Funny you should bring this up. When it came to the most recurring of Scrooge's enemies, namely Magica, Glomgold, Ma Beagle and the Beagle Boys, here's how I see it.

Magica is the overall primary antagonist of the series because she's a power-hungry witch plotting to conquer the entire world, thus making her the biggest threat to Scrooge and his family.

Glomgold is the overall secondary antagonist because unlike Magica, he doesn't possess any magic or powers. He's just a jealous and insanely greedy rival who wishes to outdo Scrooge.

Ma Beagle is the overall tertiary antagonist because she's not as magically powerful as Magica, nor as financially powerful as Glomgold. She's just a typical crook wanted by the police.

And finally, with all things stated above considered, the Beagle Boys are the overall quarternary/supporting antagonists of the series as they usually serve the roles of henchmen to other villains such as their mother, Magica and Glomgold.