Another recommendation for the Ink here. I am usually not a boutique hotel customer, but this one is good and treats elites well - upgraded from most basic to top room category as a plat last year, with many tasty goodies in the room.
Excellent location and way more atmospheric than the Novotels and Ibis.
I got a great-for-AMS €145 rate for late May in one of the sales (one of the few which allowed the use of points), IIRC about 6 months before my stay. As I recall the price for the same dates on subsequent sales was quite a bit higher, and the normal advance purchase rates around €250 a month or two before my stay.