The Boros Legion was law enforcement, the Selesnya was basically healers and people promoting unity with a hive-mind and such, the Azorious were the law makers and all three were the ones who were allowed to have representatives as a tribunal in the court of law to judge criminals.
I don't know how it changed, but the other guilds never had such legal powers: Golgori are basically the recyclers, Simic and Izzet the R&D, Orzhov are basically just a mega-corp, Gruul are a bunch of gangs/tribes with no organization that some people don't see as a legit guild, Dimir was secret for millennia, and Rakdos are basically an entire cult of Jokers and people who get off on torture and destruction.
so yeah, by original trilogy Ravnica canon, the three guilds trusted to enforce things fairly were Boros, Selesnya and Azorious. however it must be noted that the Azorious's leader Augustin IV tried to destroy the guildpact so they can put Ravnica under martial law and create place of pure order and such, so fascism by any other name in the Dissension novel, and that White mana organizations in other Mt:G stories has been fascist at times as well.
I would not rely on White mana being inherently good.