This post is about Machine Empires and my experience with them.
Contributing to the post myself, do know that I haven't played much of vanilla, my experience is mostly modded, but I do have some with Vanilla.
Modded, even with parts of the mod-making community, there seems to be a stigma against Machine Empires and I personally don't get why, part of that impression starts with Paradox themselves and the direction they've been moving in.
Currently, playing a Machine Empire is harder than playing a normal. Sure, you have to manage a positive Food income, you need to keep ontop of Goods production, and you need to make sure your people are happy. However, do all of this, and you can easily snowball, a 100% stability is truly quite ridiculously powerful, especially in the late game.
Machine Empires, however, when they manage all their Energy and Alloy upkeep, still can't as easily snowball.
First off, their most major problem is and mostly always has been the opportunity to produce Amenities, of which now only one mostly exists; Nexus Districts. Soldier Jobs CAN produce amenities, but they produce so few that it's simply laughable, while Normal empires can get away with forgoing City Districts, Machine Empires mandatorily require a few, and the best they can hope for, is to stay at 0, while Normal Empires can easily be swimming in them with a couple Civics or Traditions. The solution requires Emotion Emulators to be picked, and if you care about getting Stability bonuses from high amenities, it makes that trait a mandatory choice.
Another problem they have, which Normals have no problem with in late-game stages where it's normal for Homeworlds and early-colonized planets to have 100+ people, is Deviancy/Crime. In the late game, Machines require 1-3 sentinel posts, depending on the population count of the planet in question. If you've been taking heavy advantage of resettling to max out planets one at a time, you may even require 4 in some cases. Normals simply need 1 Hall of Judgement for the most part and they're good. Machines have no T2 Sentinel Post, and it's still sorely needed.
Machine Empires, quite genuinely also only have access to 4 Origins. They have access to 5, but I don't count Galactic Doorstop because I feel it's basically a waste of dev time to have included it, but I haven't tried playing with it. Machine Empires, due to this, don't really have any potential for variability like Normal empires have, and all of this is my problem with how Paradox have so far developed Stellaris.
They change things, with no thought to the consequence, effect, or any alternative changes. They remove Maintenance Depots, and give as much of the jobs to Nexus Districts with seemingly no thought as to how that'll affect district-heavy worlds like Agri Worlds, Generator Worlds and Mining Worlds which definitely could use more useful building slot fillers and beyond refineries, those don't entirely exist, at least not for MEs.
It's mainly just frustrating honestly to a ridiculous degree and I wish they'd at least flesh out their additions more than they do, so much in the game just lacks the fleshing out that they need to truly work.
They BADLY want Xenophilic empires be a frequently-played thing, yet they have 0 mechanics that make Xenophilic empires actually work better and support them, and anything that may be there just ain't up to snuff enough to work right. Like having one pop of each species growing at their respective speeds based off modifiers would be really, REALLY good, and allowing you to limit species and subspecies to a single specific job would be amazing, or to have a civic that allowed pops to naturally resettle based on the availability of their preferred job, and to have it function well no less.