Depends. Can your GPU push 4k 60fps consistantly? If so, do you play online games or RPGs/single-player games mostly? If you mostly play online, go with 2k 144hz. If you mostly like to play RPGs and other single player games, get the 4k.
4K 60hz is best for me. 1440p at 144hz is very smooth and nice but I prefer prettier visuals over more smooth gameplay since I think 60FPS is enough for me personally. My current rig could handle both and I have a 4K monitor so I do that instead and don't regret it. I can achieve 4K max at 144FPS+ in games like CS:GO and several other games that aren't demanding just need to wait for that 144hz 4K monitor to release.
4k will be cheaper (if the system is built/balanced properly)
4k will provide a better visual experience if that is what you like. "better" in the sense of beauty and eye candy. It will also allow you to better experience media content if its 4k compatible.
144hz will provide a smoother/quicker gaming experience, which can be a competitive advantage, but may/will require you to turn down settings in some AAA games to get there (even with a 1080ti).
Depends on what you're playing. I've been playing a lot of lawbreakers/cs/overwatch and ill take 144 over "pretty" any day. Now if I'm playing BDO or something ill take the pretty haha