Visuals: go 4K HDR, but don’t go cheap on it. A lot of 4K HDR monitors aren’t really HDR at all and will look super washed out.
Performance: 120hz refresh rate. This is probably going to be the “new 60fps” in the coming years, and future proofing for that is smart. A 4K monitor that runs a 120hz refresh rate though is very expensive right now, so go for 1440p or 1080p. You’ll lose visual fidelity and color pop that, IMO, is a major difference, but 120fps is so very, very smooth.
But as @GhostofDelta2 said, it all depends on what your PC is capable of. You won’t see an upgrade if you don’t have a GPU that can handle the higher output.
1080p 24", 1440p 27", 4k 27"-32"
These are the recommended sizes, when you are 1-2 ft away from the screen.
@Aloha_its_Kyle’s pick is the best bang for your buck 1440p 144hz monitor. It has the height adjustable stand, and I think removing the stand will reveal the vesa mount attachment. It even has 1ms at that price.
As @staindgrey stated, don’t bother with hdr monitors. They aren’t worth it atm, need 1000 nits of brightness for hdr to not look washed out, and those cost $2k+. The $300 4K “HDR” ones only get between 200-350 nits.
The price also is the lowest I seen brand new. It was at $330 not too long ago (depending on inventory).
My second monitor is at 75 HZ and 1080p, with 2 ms response rate which is what I used on my original Xbox for years with no complaints really. What I disliked towards the end was hardware related to the Xbox Bc I played for a month on my HP monitor with my PC; decent quality imo.
Sadly gears suffers in terms of NVIDIA and poor stabilization, but all my other games run like butter on the AOC.
If you’re on an XB1, it doesn’t really matter. Get any old 1080p. XB1X, you could optionally get a 4K monitor too. Same with Series S.
If you have a Series X, you have the option of going up to 120fps if you get a 120hz+ monitor, and I’d highly recommend doing that if you have the money. It’ll futureproof you as 120fps becomes the new high standard over the next few years.