Both are very good headphones; in my opinion, the 1990 is more suitable for mixing and mastering, while the 1770 is more suitable for tracking/recording on the micro. The 1770 encapsulates the ambient area more and also "leaks" less sound to its surroundings when recording e.g. guitar or vocals. The 1990 has a clear "open" sound and reproduces the music more neutrally - which is not to everyone's liking. The 1770, on the other hand, is more bass-heavy.

Both are good, it depends on what you want to do with them.

it depends, i have both. if it is very quiet at home i would recommend the open 1990 pro because they sound more realistic due to the open design, but of course they have less bass than the closed ones. for me as a gamer i prefer the closed ones, so i can hear steps in the game better etc.

Could someone recommend a headphone hook that can be stuck to the table?

If the question is still relevant, I would advise the 1990. They offer a more open and balanced sound experience. You don't hear so much from outside, so you probably wouldn't annoy anyone at home. But you can hear the outside world very well yourself, which I personally find positive, because then you don't miss any ringing or the children calling.