With the very best Apple strudel and location (Noordermarkt 43) of Amsterdam, Winkel attracts tourists and locals alike. From Spring to Fall its terrace is the place to be seen by movie stars, intellectuals, and dog-owners. (In Amsterdam these can still be one and the same person.)
The coffee is so-so, and there is no wifi (not even to be borrowed from neighbors). I am very fond of the Tostis (fried cheese sandwiches), but the kitchen can get easily overwhelmed on tropical days; so prepare for delays. The best time to visit is early in the morning and if sunny, see Amsterdam awake gloriously while reading a newspaper or enjoying a book. Avoid the place on Saturdays (upscale farmers market with folk that buy their status with biological food) and Mondays (normal market) unless one is willing to stand in line for service.
There is a decent dining menu, but I would head next-door to Noordwest, which has a slightly better food-menu (but, despite sharing an owner, does not stock the world-famous Apple strudel).
For the really hip crowd Proust is a stroll away on the other side of the Noorderkerk, but the place has nothing to offer to the coffee-sipping wifi-addict, except crowded people watching, drinks and decent hamburger.