First principles: there are no genuinely bad cameras any more. All cameras involve compromises, so it's a matter of finding the compromises that suit you best. And the camera you like more will be used more; the camera you use more will take better photos. Specifications are secondary.
Now, with that out of the way:
If you want a good camera, one that can use different lenses, then buy a Fujifilm X-series mirrorless. Pick whichever shape suits you best, and then briefly compare based on price and features, but don't make choosing a camera into its own hobby. That's easy to do, and it's not photography.
Right now, and for the foreseeable future, Fujifilm makes the most sensible line of cameras and lenses that will serve most uses for most people. Their sensor size is a nice middle ground that gives excellent quality without exorbitant cost, and the few duds in their lens line are clearly marked as such. Unless you have a really good reason to do something else, pick your favourite Fuji and go for it.
Sony does also make cameras with the same sensor size as the Fuji X-series, but if you buy one of these then you own a Sony when you could have had a Fuji. The Sony camera designs are strikingly restricted and inflexible, the interfaces vary without being improved, and their lens options are a screaming bowl of chaos. Olympus and Panasonic also make some excellent cameras with slightly smaller sensors, and different models have real strengths. Choosing among them is beyond the scope of this article.
But what if you're not looking for a camera that's merely good enough for most people?
Perhaps you're convinced that your photographic needs can only be fulfilled by a camera with a 36x24mm sensor: one that's packed with technology that didn't exist for the entire span of time from the birth of photography to a mere half-decade ago. In which case, congratulations, and let's pause for a moment of silence out of respect for everyone else in history who still managed to make meaningful work with far less than what meets your requirements.
And now go buy a Nikon D850.
The Nikon D850 is currently the best camera ever made in what used to be derisively called "miniature" format, so hopefully it's up to the challenging task of being your camera. If you have previous experience with Canon cameras, calculators, binoculars, scanners, projectors, printers, or photocopiers, then perhaps the 5D Mark Whichever One Is Current will be okay too. But really, if you're going to go to the trouble of carrying one of these things and think that creative problems have technical solutions, go all-in. Buy that D850, or whatever model has replaced it since these words were originally written.
Full-frame mirrorless cameras are starting to exist, but even at their best they're a bad match for their lenses. It's not a capability problem, it's a design problem, and not one that looks like it will be solved. If you want a complete kit that's smaller and lighter, save thousands of dollars and buy a smaller-sensor Fujifilm and its smaller lenses. If your creative vision demands "full frame" then spend what it takes to buy a top-of-the-line camera that's sized to match the lenses, which is the legacy platform that combines the best of today's electronics with fifty years of design and refinements.
Truly, the top of the line Full-Frame SLR is the Camera of Cameras, the Tool of Tools.
May it serve you well for 3-5 years before being replaced by another.
Finally, if you want a compact camera, then you're in luck because it's easy to choose. There's a huge range of styles and features to pick from, and the results are all indifferent at best. They all make pretty severe compromises in usability, design, and/or image quality, so don't worry too much and don't get too attached – pick the one that will serve you best and try to get past its many failings. Really, this is a good thing, since you don't have to worry about making a bad choice. "Bad" is a fundamental part of the product.
But whatever you do, under no circumstances should you ever buy a camera with a spinning wheel where its four-way controller is supposed to be. I'm looking at you, Ricoh, Canon, Sony, Nikon, and Panasonic.
If you can, find a compact camera with a larger sensor and a shorter zoom lens, making its image quality closer to the cameras with interchangeable lenses. Those little cameras often cost as much as an interchangeable lens camera as well, but are not as good. Bigger ones will have better controls and maybe more features, while smaller ones make better daily companions, so that's going to be your most important choice. Just make sure that your shiny new compact camera is better-enough than your phone to be worth buying, charging, carrying, using, and managing.
And phones are pretty good these days.
So instead, or as well, go buy the Fujifilm X-series camera of your choice.
Cameras are not magic. Buy one that works, which is any of them.
Buy one that you like, which could be any of them.
Buy one from a company that understands photography and likes making cameras, and demonstrates that with a clear design philosophy and a coherent product line, which is any Fujifilm X-series. Or the Nikon D850.
Or the D850's replacement, should you be reading this from the future.
In all seriousness, there are clearly major problems with this article. I'll address two of them.
First, it's only written for people who might benefit from an article of advice on choosing a camera. If you're a professional, specialist, experienced, or otherwise know what you need, then this isn't for you. What I have to say here is entirely based on talking to beginners who are looking for their first, or first good, camera. Often they'll know nothing about cameras except that they or someone they know had one once (a Nikon Rebel with a fixed zoom lens, usually) and that a friend told them that they need to go full-frame. And yes, this does happen.
Secondly, my suggestions here are intended for still photography and perhaps some casual video, for which almost anything currently available is good enough. Unfortunately for people who are specifically demanding for video, their shopping experience is about what it was like looking for good stills cameras around a decade ago. There are still some big differences in their more refined capabilities, not all of them obvious, and the compromises needed are more individual and nuanced. General advice is useless here – except to say that you should only spend about half of your "camera" budget on the camera, and use the rest for audio gear and a support or two.
And really, I do believe that what I said at the very beginning: the camera you like more will get used more, the camera that gets used more will take more photos, and taking more photos means more better photos. Compared to that the specific specifications don't matter that much.