(But then we’ll all just upvote Slaver Guilds which almost is Mining Guilds 2: Mine Harder)
Like I said earlier, Slaver Guilds is not a no-brainer. You get 10% food and minerals off tiles (assuming all food and mineral tiles are worked by slaves), but you could get the same 10% via Syncretic while being able to spec your master race into leader-related stuff and/or unity/research from the beginning. This comes at a cost of added micro though, so is not suitable for everyone. Alternatively, Inward Perfection gives you faster pop growth, and more pops produce more stuff; more unity unlock traditions faster, and some of them boost your economy too. These effects are hard to compare directly, but I tend to think that bonuses of IP outweigh SG.
Agrarian Idyll 13
Aristocratic Elite 12
Beacon of Liberty 12
Citizen Service 16
Corporate Dominion 16
Cutthroat Politics 15
Distinguished Admiralty 12
Environmentalist 12
Functional Architecture 11
Idealistic Foundation 8 (-2)
Imperial Cult 6
Inward Perfection 21
Meritocracy 14
Mining Guilds 28
Nationalistic Zeal 4
Parliamentary System 14
Slaver Guilds 16
Technocracy 15
Fanatic Purifiers 15
Mechanist 22
Syncretic Evolution 16
Post-Apocalyptic 7
Barbaric Despoilers 6 (+1)
I disagree with downvoting despoilers. Adaptability is so freaking good that I even agree to deal with militarists. A good option to alleviate their impact is to limit their share by either taking Fanatic something as second ethic, or taking Spiritualist as 3rd. Weak trait on the master race can also help; non-weak xenos or subspecies should be enslaved in the mines to have no political power.
Idealistic foundation is RP fluff which doesn't add much real value. There are many ways to increase pop happiness, so 5% buff is hardly worth a civic slot.