It depends on personal taste, but I did decide that I am never going to use a 4k screen. Way too many problems at that resolution (performance and UI scaling issues), and that it's more ideally suited for large monitors (as in 30" or more), sadly 27" is the maximum I can accept.
My choice in Swift is slightly longwinded, but in short, there weren't any IPS monitors that could come close to what I wanted on a new monitor. I came from a 27" 1080p IPS monitor (VX2770-SMH), and when I was planning on a new monitor, I wanted as much upgrade to every aspect of the monitor as possible. Unfortunately one of those was G-Sync, so options were limited: Asus RoG Swift, I had no other options.
I didn't want to compromise on G-Sync (it was my primary reason to even contemplate a monitor change in the first place), I really wanted to try it because it was new tech (I am sucker for new tech), and it was an upgrade to literally everything to my old monitor barring it was TN as opposed to IPS.
I made that compromise.
After using that monitor for a while, here were my conclusions:
1. 1080p 27" was far too grainy at my sitting distance, and I had to sit back on my chair to alleviate that graininess, which completely eliminated the point of getting a 27" 1080p monitor in the first place (would have been better to just get 24" 1080p so you have a wider range to 'sittable' distance).
2. Monitor colours out of the box is far more important than colours after calibration, because most games simply ignore any calibration you do, making it a completely wasted effort. Thus IPS is better in that regard at the very least.
3. I recently received Dell U2412M monitors for work (1200p 24" IPS) and I was sorely reminded at how much better an IPS could look better than TN, however given the choices of monitors available at the time, I had no choices. I didn't think I would want to sacrifice both G-sync AND high refresh rates for IPS, since those were the two biggest things I wanted to try in a monitor.
Due to this, I have firmly decided that I will never consider an non-Asus/MSI product again, as they are the only companies who releases top end gear in Taiwan, ironically.
My ideal monitor though remains elusive: 24" 1080p 144hz IPS G-Sync. 1080p offers a lower playable resolution than 1440p (I cannot tolerate upscaling blur), 24" should remove much of the graininess I see on 27". I just hope it'll be Asus who releases this monitor, not BenQ, AOC or Acer.