The question that arises for me is: Do you want 4K? If no, is 120Hz enough for you?
For my part, I don't need 4K and the 120Hz is enough for me in FPS games like CSGO, CoD and PUBG.
This raises another question: Is the extra cost of almost 600.- for 24Hz more and the 4K resolution worth it?
I for one doubt it, but you have to know...

You can view both monitors via the comparison function. The PG43UQ is simply a bit more powerful. My PG349Q with its 120 Hz and the rest of the specifications is absolutely sufficient for me. If you're looking for a 1ms monitor, go for the PG43UQ.

I've had this monitor for just under 2 weeks now and I'm thrilled. I find the 34" ideal for the desk. If the screen diagonal were even larger, I would have to somehow get more distance to the screen. I use the monitor both for gaming and for working and it works perfectly.