You should answer the question of what is more important to you.
Higher resolution and sharper image (1440p) or smoother display? Here comes the preferences and habits.
Between 240Hz and 165Hz, you'll see the difference, but it's not as striking as the one between 60Hz and 120Hz or 144Hz.
For professional gaming, higher Hz seems to be more important than resolution.
In particular when it comes to CS: GO As it is well known, a larger group of professional players play at lower resolution
to have larger models of opponents and more FPS.
On what settings have you played so far? What PC components do you have?