Wich Colorimeter

I am looking for a decent Colorimeter.

I want to Calibrate the BenQ XL2420T and the Samsung 970D and Dell U2412M.

Anyone who has some advice wich one to buy? Spyder or ?

I recommend Chroma 5 (fast and very accurate). With some luck, you may find one on eBay.

Kinda expensive

They Eye One Display Pro, aka Eye One Display 3. Not the cheapest, but very fast, and reliable measurements. Cannot be beat at even twice its price point currently.

For non-professional use, I don't see much point in getting the i1 Display Pro. You can get the same quality from Colormunki Display, just at slower speed, but for people who only calibrate once a year, it's not an issue. The Colormunki is supposed to be artificially crippled by X-Rite's software to prevent it from clearly being a better value than the i1, but it's supported by Argyll CMS, so that's not really an issue any more.

The same is true for the Spyder 4 Express vs the Pro/Elite.

Colormunki produces somewhat better results than Spyder 4, but they are close enough for most people that the lower price of the Spyder 4 probably makes it a better value.

ColorMunki Display for basic needs. i1 Display Pro if you want more flexibility.