When buying a new monitor there are 5 sites you should have open at all times:
1. The site selling monitors (eg plattetv.nl)
2. The comparison site Display specifications which allows you to search for models, add them to comparison lists and then view detailed specifications next to each other
3. A google search for the reviews of the model
4. AV Forums to search for good or bad experiences with the model.
5. Your price comparison site (eg Tweakers Pricewatch

Also useful are sites that tell you what each model means, how the model number is built up. For Samsung you can use This site

The important specifications are:
What type of panel is it? (IPS / VA / PQL / etc)

Panel bit depth: is it 8 bits, 10 bits native or 10 bits (8 bits + FRC)

Colour bit depth: 30 bits?

Resolution: native UHD 3840×2160 pixels

Pixel density: higher is better

Display area: bigger is better

Static contrast: more is better

Response times (minimum / average) and input lag (for gaming): less is better

3D: if you think that’s important

frequency: most are 60Hz, some are 120Hz (higher is better)

Interpolation value: most are around 1200, higher is better

Power consumption: less is better

Other features: connectivity (what kind of USB ports (3.0?) etc fit in), sizes, colour, stand size at the back, network (does it do 802.11n 5G and 802.11ac?), features (does it have a good 4k upscaler, how black is black, what kind of colour enhancements does it have), etc.

Good luck!