Hey,That would also depend on your budget. Something with an IPS screen, at 144hz and 2560x1440 resolution is where I'd be aiming ideally.
The cheapest monitor I found with these specs is this one : ViewSonic LED VX2705-2KP-MDH 27" at ~ 326usd
ViewSonic VX2705 2KP MHD
is it a good monitor, and the price, what do you guys think?