As far as new ones last I heard they were all being made by a couple of companies and re branded so it probably doesn't matter much what you get. Id base it on reviews and how long a certain model has been around.

The one I'm using I got from a friend at work. It's newer and has the rounded shape to it but still only has one knob like the old style ones and none of the electronic junk. It has a fan that runs the whole time it's on but you can hear the noise it makes changes slightly as it cycles on and off. I have it on the lowest setting and it keeps the humidity at a decent level. It has a drain hose that I run into the floor drain so I don't know how often it would need to be emptied.