Which 240Hz IPS is the one to go of these?

[Only1]

I didn't like the colors of the xg2431. The gamma looked a bit wonky too. The main reason i returned it was the strange headaches i was getting while using it.
If you don't mind 27" monitors and have the budget, i suggest trying the 300hz 1440p ASUS XG27AQMR.

I would be wary of the XG27AQMR. I used another monitor with the same panel, the Acer Nitro XV272U KF, and it was not a great monitor. It gave me eye strain, and it had poor brightness uniformity. The center of the screen was noticeably brighter than everything else, and it was very annoying.