The best dehumidifer is the one you find second-hand. We have been happy for the past 6 or so years with a secondhand Whirlpool one we got via the classifieds.
It recently started leaking though, and I'm happy to say this was an easy fix -- just needed the drain to be cleaned of dust!
One has been sufficient for us in even over 600 sq/ft.
The clothes drying function is useful -- it just blows more hot air.