Myntekt :
I'm a casual gamer, I'm not sure if I should get IPS or 144hz. My budget is from 250€ to 400€
While answering questions about monitor purchase I usually give the same advise - if there is any showroom/store nearby go there and spend some time in front every monitor. Compare the feeling you get from IPS, TN. Compare refresh rates.
You will know what you like the instant you see it. Some things on paper look great, sometimes people would praise products and you might end up hating it.
Some time ago I bought a BenQ XL2420T -
http://benq.co.uk/product/monitor/xl2420t and was so excited about it because back then was one of the few 120 Hz monitors on the market but the moment I plug it in and sat in front of it it gave me such a horrible headache I never had before. I had the feeling needles were going through my eyes and deep into my eye sockets. I spent 2 whole days calibrating it and adjusting every possible setting to no avail. At the end I ended up returning it. So as you can see it's hard to tell.
Edit: I am using Acer GD245HQ 24" 120 Hz Monitor so the headaches weren't caused by the 120 Hz refresh rate.