I stayed at The Flying Pig Downtown when I was there last summer. It ended up being the best hostel we stayed in during our time in Europe. It's very central, close to the red light district, supermarkets, musuems, lots of coffee shops... etc. The rooms are very nice and they offer queen size beds if you're traveling with a partner, or just want more room. It feels very safe and secure. There's a fully equipped kitchen downstairs and the main room has a bar and lounge area. If you're planning on visiting Amsterdam and want to see all the major sights, I definitely recommend the Downtown location.
http://www.flyingpig.nl/hostels/flyingpigdowntown.shtmlThey also have a beach and uptown location.
I recommend booking in advance for every night you want to stay there. It's very popular, and booking on a day-by-day basis like we did means that you'll probably end up walking around Amsterdam looking for another hostel. We stayed in another hostel our second night in town and it wasn't nearly as nice.