Everyone has different needs and values different things. If you're looking for the "best" at something, you often have to sort through mountains of other information, so I'm going to take a stab at maintaining a page with some of the more important factors people look at.
Before proceeding, let me first put on my bullet-proof vest and then my armor system on top of that, then crouch behind the three foot walls of my bunker…
- Best Autofocus. The Nikon Z9 and Sony A1 represent the current state-of-the-art in mirrorless focus when tracking subjects at high frame rates, though they have not quite equaled what the Nikon D6 DSLR can do in some situations. The Canon R3/R5/R6/R7 and Sony A9 Mark II have probably the second best. The Nikon Z6 II and Z7 II are a close third, along with the other current Sony A7 models. The Canon R/RP, Fujifilm X-T4/X-H1, and the Nikon DX models all have very good continuous servo autofocus, but not yet to the level of the best DSLRs or even best mirrorless.
- Best Low Light. The Sony A7S Mark III is the clear winner here on a per pixel basis, with the Nikon Z6 II, Panasonic S1H/S5, plus Sony A7 Mark III and A9 Mark II also quite good. The advantage of full frame and those Sony Exmor sensors can’t be denied. And frankly, any current full frame camera measured at typical output magnification, should be nearly equal to the others. While many claim APS-C Fujifilm is at the same place as full frame Sony, it isn’t.
- Best Dynamic Range. A log-jam if approached purely from measurements. For crop sensors at base ISO you've got many strong contenders for wide dynamic range: Fujifilm X-Pro2 and X-T4; Nikon Z50, Olympus E-M5 Mark III, E-M1 Mark III, and Pen-F; OMDS OM-1; plus the Sony A6100, A6400, and A6600. But overall, the larger full frame sensor in the Sony A7 models changed the game here and the Mark III models pushed that up some more: they’ve got better dynamic range and now we can get uncompressed raw data, too (note I wrote Mark III, not Mark IV ;~). Nikon matches that with the Z6 and Z7 (and II models) plus Z9, and it appears the Panasonic S1, S1H, S1R, and S5 do, too. Technically, the Nikon Z5 has a bit more dynamic range at base ISO than the other full frame cameras, but that advantage goes away at higher ISO values. The medium format Hasselblad X1D and Fujifilm GFX now push dynamic range out a bit further, too, and currently represent the best of what mirrorless can do. Still, I personally would contend that at base ISO you'd be quibbling over unimportant nits between most APS-C or larger sensor cameras, and that we've got plenty of dynamic range with most recent mirrorless cameras for most people. While "dynamic range" is often cited by people as the reason they favor camera X over camera Y, in reality I think this is chasing the wrong suspect. Even more curious is how many people who say they want more dynamic range also select higher contrast settings or post process to add contrast, which tends to remove all that extra captured information. Make sure you really know why you want and need more dynamic range before using this as a criteria for evaluating cameras. Caveat: dynamic range is measured and evaluated differently by virtually everyone, and modern cameras now do slightly different things at higher ISO values that may change your decision.
- Best Resolution. The Sony A7R changed the game initially, and the current A7R Mark IV pushed that game further to 61mp. Sony also has the 50mp A1. Nikon pushed their Z7 and Z9 models to 45mp. Panasonic pushed it to 47mp plus added pixel shift. Those are currently the highest resolution full frame mirrorless cameras by a fair margin (though the medium format Hasselblad X1D and Fujifilm GFX now top the full frame ones with 50mp and 100mp options; they’re in a much higher price class, though, and use a different sensor size). Frankly, I think you're splitting hairs with any of the 45-61mp full frame cameras: they all are high resolution enough that handling and lens issues will play a bigger part in how good your results are. Some Olympus and Panasonic cameras have a mode that allows them to take high resolution images on a tripod by moving the sensor for multiple continuous images that are then converted into a single image file (as do the Sony A1, A7R Mark III and Mark IV, and Fujifilm GFX100). This, too, produces very high resolution, but I can’t consider it “best” because it’s not useful if there’s any camera or subject motion. Caveat: watch out for diffraction, which will tend to visually steal back some of the resolution you may capture. And at these levels, you need good lenses to fully capture what the sensor can record.
- Best Video. For awhile this was a total no-brainer: Sony Alpha for consumers, GH6 for the pros. But because the HD TV bar—even for 4K—isn't set very high and everyone has been adding more video capability with each generation, it's not so clear cut any more. I suspect that the "convenience" of video is now more important than particular performance aspects for most people. Thus, the Fujifilm X-Pro2 and X-T1 were not winners because video was buried on those cameras and had impacts from the early X-Trans sensor use, while many of the other contenders made recording video easier. The Fujifilm X-H1, X-T4, and X-S10 correct much of this, so even within a model line you can often find “better video." For outright capability the best overall choice is probably now the Nikon Z6 and Z6 II (surprise!). Not only do they have exceptional 4K in-camera capabilities, but the (optional upgrade fee) 10-bit N-log external and raw capability is as good as I've seen. Moreover, the Z's autofocus is the best I've seen on any of the mirrorless cameras for video. That said, the Panasonic GH5 II/GH5s/G6 and S1/S1H/S5, plus the Sony A1, A7S Mark III, A7C, and A7 Mark III also produce exceptional video. Canon was first to 8K with the R5, but the heat build-up issues make this a conditional usage. Nikon beats the heat and much more with their 8K in the Z9, which can record raw, ProRes, and 10-bit 4:2:2 N-Log. Note that we now have several video-only players, such as Blackmagic Design, which also warrant a close look. If you’re talking 4K video in low light, the Panasonic GH6 and Sony A7S Mark III are probably the best choices at the moment. Caveat: a lot of the smaller cameras overheat when doing video for any length of time, most have time restrictions on clips you want to be aware of, and all of them have fairly poor microphone amplifiers in them.
- Best JPEGs. Probably the most subjective category of "bests," as we all have different preferences in terms of color, contrast, and more. Heck, many of the males reading this have some form of color blindness, which will certainly impact how you evaluate an out-of-camera JPEG. That said, the Olympus mirrorless cameras have consistently excellent JPEGs in my experience, especially if you take the time to tweak the defaults a bit. The Fujifilm models also produce superb, highly regarded JPEGs. Caveat: but those nice looking JPEGs from the Olympus and Fujifilm are not color, saturation, or contrast neutral. Moreover, virtually all the cameras allow you to tweak the look of JPEGs in ways that would allow you to get a look you like. Technically speaking, I don't think there's a best here unless you're lazy. Also, watch out for Auto White Balance. Some systems, notoriously Panasonic, don’t do so well in setting the correct white balance.
- Best Lenses. The m4/3 system still wins, due to both choice and quality. Fujifilm gets a strong nod of appreciation for producing excellent lenses with a reasonable large choice. But Fujifilm needs even more choice, especially at the telephoto end. In my estimation, Sony APS-C is still somewhat let down by their lenses, though Sony has been addressing this for vlogging type uses lately. Sony full frame now has a wide set of excellent lenses to choose from and excellent third-party support. In terms of optical quality, Nikon has pretty much been hitting home runs with their Z-mount lenses, and Sony has now upped their game, as well. If you're one of the 1%, Leica might take the cake for lenses here, but I'm pretty sure that less than 1% of you reading this are in the 1% ;~). Caveat: this is a "best" that is in constant flux, and if you have a particular focal length preference (or preferences), you may be best served by one mount over another. For example, the Zeiss 24mm for the E-mount APS-C was about the best 35mm equivalent option out there, and clearly superior to the Olympus 17mm, but the 35mm FE-mount Sony Zeiss outclasses both, and the Nikon 35mm f/1.8 S tops even that.
Update: This articles used to also talk about the worst choices, but the levels of all competitors have risen high enough that I no longer believe that useful to talk about.
