Really no such thing as 120Hz. It's a gimmick. It's all still 60Hz. What happens is you have 1 frame per second at 60Hz. With 120Hz, it'll show the same frame 2x a second. To the viewer it just makes for a little less ghosting appearance, and this translates to apparent smoother motion. Does nothing for details.
If your game play is mostly fast action games like gta:V etc, a 1080p/144Hz monitor makes sense.
If your game play is slower strategy, sniper, mmorpg games, then a 1440p/60Hz would be better.