I purchased the Asus PG43UQ. So far I am quite happy with it. I won’t claim it’s perfect, but it is one of the best monitors I have used over the last 40 years, so there’s that. I use mine for work, gaming, and watching movies and shows. And so far it has performed all of those tasks quite well. A word of warning, running a 4k screen requires some grunty hardware, or performance will suffer badly in games pushing that many pixels.
Here is a video review of the PG43UQ (I think wendell has had experience with it as he referenced it in a recent video, but he has not posted a video for it yet.)
My monitor had zero dead or stuck pixels, which is quite amazing. Either the quality control is very high, or I got supremely lucky. As I have not seen others complaining of dead pixels, I suspect Asus quality control is quite good on this monitor.
The speakers are decent for monitor speakers, but will not compare with a real speaker setup of any sort (get real speakers if you plan on watching movies).
It can be VESA mounted and the brightness is great for working in a well-lit room or even in rooms with sunlight. If you use it in a dark room you will need to turn down the brightness or it could be blindingly bright. I personally use a HumanScale M10 fully articulated Monitor Arm, but those things are hella expensive. I believe there is another company out there that makes a fully articulated monitor arm which can support these large monitors, and their prices are much more affordable than HumanScale. I can’t remember the name off the top of my head though. (I remembered the name! Ergotron - added another reply further down the page in case you already read this post and won’t notice this edit)
It is not an OLED, but I view that as a positive because I do not have to worry about any sort of burn-in from leaving the screen on, or from having static elements, for long periods of time. (If you are using this for work on a PC I strongly suggest avoiding OLED’s for now, see wendell’s and linus’ recent videos about OLED problems for more info on that).
I do not know if it is still available new, but I see quite a few used and renewed ones on amazon. (correction, I DO see new ones on Amazon for a decent price, as it is over a year old now, the pricing on it seems to be reduced? I paid around 1600$ for mine about halfway through 2020. Currently looks to be around 1k in price.)
I have not had any problems with mine, but I did read some comments that dealing with ASUS customer service can be difficult, so take that into account if you think you may run into problems.
I have not had any personal experience with the DELL versions but every time i have dealt with DELL as a company for support, i have always had poor experiences. DELL sucks really bad for customer service imo. But perhaps your experiences will vary.