I head through the AMS airport one a month with at least a four hour connection. During the morning rush hour I've always waited 45 minutes or longer for the Worldclub showers. They are nice facilities.

The mercure facilities include a toilet and a little more room and are equally as nice in my opinion.

Personally, the yotel hotel is the only way to go if you're going to be there around four hours. You get all of the above plus a nice bed, tv, and privacy. Just MHO....