Do u have anything else yo suggest is the 100 euro difference worth it or should i go for viewsonic?The ASUS is the better monitor, but both are pretty decent. If you game in a dark or low light environment, you could have problems with either of these as one has poorer black uniformity and the other lacks having really good brightness characteristics. For normal light environments, either one is probably fine though. Look at the Rtings reviews here.
https://www.rtings.com/monitor/reviews/asus/tuf-vg27aq
https://www.rtings.com/monitor/reviews/viewsonic/vx2758-2kp-mhd
Those pretty much tell the tale.