The problem is, G-Sync makes a big difference in the price of most monitors. I don't currently know of any G-Sync monitor that can keep up with this price/performance ratio.
I bought an Acer Predator X34A (34", 3440x1440) myself because of G-Sync, without G-Sync all comparable monitors were about 100-300 francs cheaper at the time.

The monitor is certainly also good with an Nvidia card. It depends more on what you need the monitor for. G-Sync and Freesync are especially good for fast movements in games. Professional gamers swear by these techniques (I'm not a professional gamer, but I can see the difference). Casual gamers or others usually don't care or hardly see the difference.