Bobbythedoggy :
Lannister in the North :
It comes down to personal preference.
The 144Hz will look a lot smoother, the animations will really pop off the screen; It is my personal preference.
The 4k one will be more detailed, more rich pictures in a per frame basis.
The 144Hz monitor has a nice and low response time of around 10ms (without overdrive) in line with decent TN panels. Which is important when playing twitchy games like FPS's where reaction is everything.
I haven't seen the spec for the 4k, but i wager the response time isn't nearly as decent.
EDIT: Which 4K monitor is it? Can't seem to find a 4K Acer Predator with IPS. The one i did find was TN (and still had worse response time than the 144Hz)
It's this one I found in Linus' review
http://youtu.be/_LTHr96NueA
Edit:Oops sorry,what I meant is that the 4k version is 60hz but I think it's IPS
He mentions the XB280HK, which is a 4K TN monitor, with a link to a review he did of it somewhere in the beginning of the video.
He also specifically mentions it being a TN panel:
https://youtu.be/_LTHr96NueA?t=104
So it's 4K TN 60Hz vs 1440p IPS 144Hz;
You still have to choose between 4K or IPS.
Your GPU will handle 1440p much better than 4K as well, meaning higher framerates.
Together with 144Hz this will mean much smoother gameplay.
The XB270HU is the clear winner over the XB280HK imo.