Oh boy! A chance to rant! I'm so there!
I'm sorry, as a Nintendo fanboy I'm contractually obligated to recommend you get a Switch, chow chow.
Seriously though, just how much do you want to play Nintendo exclusives? That's kind of the first question you need to ask yourself. If you can't do without Mario/Zelda/FE/other Nintendo franchises (and the odd exclusive third party game), then your choice has already been made for you. No need to even consider the other two.
Personally, I enjoy the mobile aspect of the Switch, playing during my daily commute or whenever I have a bit of time during breaks is great. Depending on how much time you spend on the go or commuting, this might also be something for you to mull over.
Next is the Japanese/weeaboo stuff. You a fan? Nintendo might have a Vita successor at their hands, and the console is region free. So that's kind of a huge plus in their favour, provided Japanese Devs continue to find success on the system - which is not guaranteed by any means.
If you came out from the above issues without a decision for Nintendo, then go with Sony, can't really go wrong there, although theirs technically is a region locked system. MS has practically given up on that front after decades of anaemic at best sales, so don't get an Xbone if that's what you're after.
Are you outside of the US? Be aware that you will be a second class citizen on MS systems. It's not egregious, but ever so often you will notice a lack of content, features or support, more so than with the competition. Whether that even bothers you is a matter of personal preference.
Otherwise, how proud are you of that 4K screen of yours? Currently, only the Xbone X will come close to pushing enough pixels for the full 4K experience, barely. A PS4Pro will always be just a bit behind unless Sony spends the big bucks. *cough*getagamingPCifthatsreallyimportanttoyou*cough*
Also: If you want to max out your 4Kitude, a switch must never even enter your thoughts. EVER.
Another way to decide would be the controllers. Walk into any shop with demo units and get a feel of those. Switch without the ~80$ Pro Controller is a pretty basic experience. It works, but you will probably want one, eventually. The Xbox controller and Switch's Pro controller are pretty dang nice, although the latter has no analogue triggers (and the dpad is kinda not up to usual Nintendo standards, but that's debatable). PS4 has the Sony setup with regards to the placement of the analogue sticks, which might annoy you, and it has a distinct shape that might or might not be comfortable to hold for you. Depends on your hands. So grab those fuckers and play a bunch of rounds of whatever is on those demo units.
Last, get a load of the UI. Personally, I'd rather have nails driven through my noodly appendage than suffer through whatever redesign MS is currently throwing at their console this month, but the PS4 menu ain't exactly perfect either. Both are kinda overfraught and up their own arse about design philosophies/have problems with how to grant you quick access to functions while still serving ads and offering alternatives. Nintendo suffers from the opposite, their OS is incredibly barebones, simple to a fault. I'm more of a fan of the Switch OS, but it definitely has it's own share of issues, so YMMV. Once more, demo unit time. Or bother friends or watch YouTube vids.
