There is no correct answer here, just a question of which you think is going to be better for you.
A 1440p monitor is useful outside of games because you have a lot more desktop than a 1080p, and the greater PPI means stuff will just plain look better in and outside of games. More than likely it will also have an IPS panel, so you get better colours as well.
A 144z monitor can support 3D gaming, or just plain run at a higher refresh rate which will make on-screen action (particularly turning in FPS') a lot smoother.
Both will come with a performance hit (kinda, the 144hz more shifts the minimum level of acceptability up) so you need a card that can handle it. An Nvidia card would lean toward the 144hz as then you have the 3D option open to you (AMD has a 3D option as well, but nowhere near as good as Nv), while AMD leans toward the 1440p because they just perform better at higher resolutions.