As per the topic! I think it's interesting to hear what sounds 'work' for other people, whether they find it soothing or they develop sensations of frisson. Of course, whatever is best is subject to personal opinion. I'll go first.
I'm very fond of clinking sounds created by ice. Particularly when a few cubes are swished around in a glass or listening to it being stirred in coffee and tea.
Other natural water moving sounds are my runners up. Rainfall of any variety, as well as ocean waves relax me. Running tap water and the like don't give me the feeling, but it's kind of enjoyable to listen to boiling water when you're making something in it, like potatoes.
How about you?
Absolutely rainfall for me. I struggle to sleep without noise and usually sleep with headphones and the Rainy Mood app.
I also want to mention an art piece that I'll never forget. "Clinamen 2013" by Celeste Boursier-Mougenot is a circular pool of water with porcelain bowls of various sizes floating on the surface. The bowls are allowed to drift and bump into each other, making soft chiming noises. I think it may be one of the most beautiful sounds I've ever heard.