What is better?
A 4k monitor with 60Hz
or
a WQHD monitor with 144Hz
and why?
I would mainly use the monitor for gaming, YouTube and Netflix.
I generally prefer higher frame rates. In addition, 4K is overrated for your application areas. That makes sense only in productive environments.
WQHD and 144 Hz
Why?
Advantages in every game and normal application.
4K just looks nice, but since you have rather lower FPS tend to look in faster games.
So in short: 4k looks awesome (if movies or videos support this too) but also requires a lot of power. That If you're primarily a shooter, where the graphics are not so important and you need more frames - rather WQHD. I find 144 fps very important for faster games. For other games, where eg Aim does not play a big role and the game experience is created by nice graphics, is probably 4k better. But you probably will not be able to play at maximum graphics settings. What kind of graka do you have?
I have a 1080Ti, this should actually be enough.
Yes, that's a sensible graka. But even so you have at 4k, especially in elaborate triple A titles, the graphics a little throttling - more than WqHD. So either many nice fps for fast games or a better resolution with less fps and lower graphics settings.