Both are as good as each other. 144z means better refresh rate than 60Hz which results in better fluidity of motion. This wont have a massive effect on quality however if you have vsync turned [ON] then you can play at a constant 144FPS.
If you have a graphics card that can performs upto resolution of 1440p then get that as your gaming experience will be better.
I personally like a monitor which could perform at higher resolutions.