I have the Trane-branded version of the Aprilaire 600 evaporative humidifier and it works pretty well. Very simple, low maintenance. On down side, it does "waste" a lot of water due to being designed to continuously flush itself to keep from getting gunked up with deposits. Also it gets my house up to about 35% relative humidity (RH) - and sometimes I'd like to see it a little higher.
For a while I had a different type of humidifier that had rotating plastic discs that dipped into a water reservoir, and air blew over the tops of the discs. Seemed to be a little more effective but the reservoir would get mold after a while.
I have thought about a steam unit but they are expensive and at least the initial versions had a lot of problems as I have read on another list. I think one of the advantages of steam is that is can get more water into the air than evaporative units, especially if you have a heat pump -- heat pumps put out cooler air than gas furnaces so it is harder to get water to evaporate.