Mechanist 33 (+1)
Mining Guilds 29 (-2)
There's clearly two schools of thought here. Let me try one last time to convince people - mechanist gets you more pops faster, and thus more tiles worked faster. Mining guilds only has a starting advantage of 5% minerals over mechanist, which at the start amounts to a paltry ... 0.5 minerals per month. A single robot pop that is produced in excess of the Mining Guilds empire will already cover that, once it's done paying for itself ... which it will very rapidly. On top of that, do not underestimate having free starting technologies - the path to droids is shorter, thus enabling colonizing every single last uninhabitable hellhole in your territory that much earlier, for even more minerals. And last but most certainly not least, there's the 5% robot upkeep reduction you get from Mechanist that you can't get anywhere else, which lets you squeeze out that little bit extra energy efficiency that you just can't get any other way.
Yes, Mining Guilds allow for a wider variety of civics and are less restrictive, and are thus better for a general playthrough. But if you're specifically aiming to beat the crisis in the most optimal way (which, may I remind people, is the premise of this competition), the sooner you get the snowball rolling the better off you are. Mechanist lets you do that more so than Mining Guilds due to the extra pop growth and the tech reductions. With that said, clearly, Mining Guilds is the mandatory other civic of choice.