I am an opinionated knitter in Amsterdam.
They only have Manos del Uraguay, but they have a very nice selection at decent prices. This is an excellent addition to the poor selection of yarn stores in Amsterdam. And the rest of the store is fabulous.
While Sylvia's has a good selection of Lana Grossa yarn, it's cluttered and uncomfortable to be in there for very long. And most of the yarn is in places where you have to ask to see it. Lots of other craft stuff - and she seems to try to dress the place up. Just too much stuff around. Don't go. It's horrible. Skip skip skip.
It's a fine yarn shop. The customer service is what sucks. The first comment is years old. It WAS the nicest yarn shop in the Center of Amsterdam. Now...not so much. But it's cute and expensive, if you like that sort of thing.
Lots of great new yarn you won't find anywhere else in Amsterdam. Always friendly service and a great knit night on most Thursday evenings. (Check the website for the exception. I think it's the second Thursday in the month.) A beautiful store in a great location.