Hello! As someone who has been gaming for the majority of my life, i have seen the evolution of visuals and technology from CRT to the current IPS/TN panels. In my younger years i was an FPS and RTS nut, and now i mostly play RPG / Action Adventure games. Here are my thoughts :
Will you notice 144hz? YES. I notice it just moving windows around on the screen, everything is smoother that your system can render quickly enough. Even the mouse moves smoother. Is it a huge difference over 120hz? - No.
I recently switched from a 1080p 120hz to a 1440p 144hz gysnc monitor. Both of these are TN panels, and both were over 500$. If you are staying under 500$ get a great 1080p 120hz monitor. If you are going to spend over 500 i would wait and get a 1440p monitor. Whether you go 60hz or 144 is up to you. At 1440p your set up will probably not be able to push much more than 60fps anyway, so getting a 144hz monitor at 1440p is probably a waste; but if you plan on upgrading it would be a good way to future proof your display.
Just my 2 cents! Also, if you value colors over response time, go for an IPS panel instead of a TN panel.