Ryzouk :
So you think I would notice a great difference between the monitor listen and a G sync one ?
Just to be clear, G-Sync (and FreeSync for AMD) function a bit differently than increasing refresh rate. They're for eliminating tearing and judder. Normally the graphics card constantly updates the image one horizontal line at a time, overwriting the previous frame as it draws. When the monitor timer says it's time to refresh the screen, it grabs and copies the latest version of the image for display. If this sync happens while the image update line is anywhere other than the very bottom of the screen, you get a tear. The upper half is of the image is for the current frame, the bottom half is for the previous frame, the disjoint in the image where the two meet (line which is currently being drawn) is called a tear.
V-sync eliminates tearing by using a second image buffer, so only a completed frame is ever displayed. But that introduces an extra frame of lag, and can result in judder if the framerate drops slightly below the refresh rate. One image is shown for two consecutive frames, which can be jarring for the motion detection cells in your eyes as an object which is supposed to be moving at constant speed momentarily freezes.
G-sync and FreeSync eliminate tearing by making the monitor sync (refresh the image) whenever the GPU completes drawing a full image (sort of - the details are a bit more complex). It's basically a variable refresh rate. The result is tear-free images without the lag introduced by V-sync. If you're bothered by tearing or judder, then G-sync is definitely a feature you want to consider. If you don't notice these things, then the extra money for G-sync is probably wasted. That said, all other things being equal, I would opt for G-sync over 144 Hz.