Not clear if monitor or mouse.
Mouse dpi: I'd go for ~1600 but it maybe preference with your movement sensitivity. Ideally you keep 1:1 mouse dpi it's sensing per monitor dpi. For too high dpi, you lower the sensitivity which just removes info so makes it useless. Too low and it needs to add info which can cause jumping or not sensing in the first place depending on the surface.
Monitor dpi: Also the distance you sit away or screen size may play a role in just how high you want it because some things may get small if the game has bad high dpi scaling. This is really dependent on what you like, what you have space for, and what you can afford. Go to a store and look at the monitors in person.