JinKazaragi: I wouldn't buy a display below 144Hz anyway.
As for the resolution, on a 24" display I'm completely fine with 1080p. And I can't go any bigger than 24" because there wouldn't be enough space on my Desk.
I plan to change that situation in the future, but that'll still take 1-2 years.
There are 24" displays with QHD (but not that many unfortunately). I am using one in fact because 27" is a bit too big for my tastes too. I upgraded from a 21.5" 1080p. The DPI and hence the detail on that thing is incredible. But some people might have trouble with web pages, icons and texts in general being a bit smaller than usual.
StingingVelvet: Yep, once I got a 144hz monitor I was amazed at what a difference it makes. Playing F.E.A.R. right now at 144fps and it's so lovely. It's much better than 4k60fps, and a reason to stick to PC since I'm sure console games will always prioritize graphics over framerate.
However keep in mind it's hard to run modern games anywhere near 144fps, and a lot of older ones break above 60. You'll only be able to enjoy 144fps like half the time (with singleplayer games anyway). I started a thread a while back about my frustration with this, because 144fps is so awesome it sucks to not have it all the time.
I have a 1080ti and even most newer games sit comfortably above 100 FPS on max graphics. Most recently RAGE 2 which was very smooth. That would be unthinkable at 4k.
And playing UT2004 on 165 Hz is something else. I got noticeably better since I upgraded the monitor.
It is still going to be a few years before we can run 4k at decent frame rates. Until then, 1440p is where it's at currently.