I wanted a studio apartment with a kitchenette and easy access to the main sights, and found it at Oberhaus. It is in a chic residential neighborhood slightly north of the city centre, and is on a bus line with frequent service and close to a metro station. The room was very bright and comfy with all the necessities. I also asked for and got a toaster, extra pillow, ethernet cable and iron/ironing board. You can also have a microwave oven on request.
Be aware that this is a block of apartments and not a full-service hotel, so you don't get room service or 24-hour assistance. The reception is open M-F business hours and Saturday restricted hours, although I think there is a housekeeper on call if you need something urgently. My one complaint would be the flimsy lumpy pillows, but I think that's a German thing so I didn't bring it to the attention of the staff. There is a sauna which I didn't use, and a free washing machine and dryer in the basement. They offer a breakfast buffet, which I didn't take since I had my kitchenette.
The staff was very pleasant and efficient, even going to the trouble of planning and printing my journey to and from work from the public transport website and recommending restaurants.
I paid 100 euros/night, which I think is quite reasonable for Hamburg.
I can definitely recommend this accomodation for work or pleasure.