Thank you all for your answers.
Is it even OK to buy now GPUs, since the prices dropped and profit is much lower than 1-2 months ago?
What do you think its good deal for a GTX 1060?
Is it better to grab 3gb version for 240eur or 6gb version for 290eur?
If you want density of the rigs, the nVidia 1080ti is the best. The dollar/hash is not too high.
Isn't it better to get 2 of 1060s for the same amount of money than one 1080ti?
Furthermore, 2 1060s are cheaper than one 1080ti and give more hash power.