Nobody mentioned panel type yet, but that's one of the more important factors. There are a lot of names, but you basically have four choices:
TN: cheap, fastest, but awful viewing angles and colour shift. Iffy white and black levels.
VA: arguably slowest, wide angles and very saturated colour. Best black levels other than OLED, white less perfect. Ideal for films.
IPS: slightly slower than TN, good viewing angles, best colour reproduction. Best white levels other than OLED, but black less perfect. Best affordable all-rounder.
OLED: viciously expensive, perfect viewing angles, perfect colour and black and white levels. If budget is no issue, take this - but likely to be a factor 10 more expensive than the others.
Note that "speed" here relates to the physical switching from grey to grey, it's not an indicator of (input) lag. A slow screen will ghost on very fast movement, but you will see the movement straight away. Input lag is a different category and is determined by the screen electronics, not the panel type. Generally, the more processing a screen does, the higher the lag - that's why televisions are less ideal for gaming. Input lag is possibly the worst factor for gaming, but there are no good specifications to determine it, you need a good independent review comparing the exact model you want with others to determine it, regardless of panel type. You are better off with a slow VA panel with low input lag than a 144Hz TN panel with input lag in the tens of ms (and yes, even in that category they exist).
Personally I can't stand TN panels and their shifting colour as soon as you move your head. My go-to screens are Dell 'business' IPS screens. Good build-quality, decent price, no nonsense and fast enough that I don't notice any lag or ghosting (but I'm not an FPS gamer, my reflexes are not what they were 25 years ago and even then I was nowhere near a pro). I forget the exact model # I have now, but it's a QHD (2560x1440) resolution screen that pairs nicely with my GTX1070.