The first and most important thing is to ask yourself what you want to use it for.
If you have two monitors then you might want to complement what you can already do well with the other one.
If you can have only one monitor you will want to prioritise a decent QoL product over something that squeezes out 5ms more reaction time for some autistic circle clicking game.
With QoL I'm talking about things like viewing angles, colors, durability, adjustibility of height/angle, low blue mode and whatever, things that actually matter a lot.
Believe it or not, I use monitor settings that are likely to decrease my performance simply because I find it much more comfortable looking at a screen with lower to medium brightness than full brightness.
Here's a fancy site to calibrate your monitor learn a bit stuff about LCD screens:
http://www.lagom.nl/lcd-test/
This website has quite some information on motion blur, although that might be more relevant to the other gamemodes, click around a bit:
https://www.blurbusters.com/faq/motion-blur-reduction/
Logicalincrements is a website that recommends PC parts fitting together at reasonable prices or something. They have a separate listing for monitors and also a FAQ at the bottom of list which you might want to read through:
http://www.logicalincrements.com/monitors