This model by Aprilaire uses steam and is what I would suggest you take a look at if you have not been satisfied with lower end humidifiers.

Here is a link that might be useful: aprilaire steam humidifier

I have a general aire unit that works well.

In duct humidifiers are only as good as the run time of the furnace. If you have a well insulated home and few cycles per hour it's not going to do much for you. Misters are nice if you don't have hard water, but high maintenance if you do.

Actually the aprilaire steam model I noted above works electrostatically.....the harder the water the better.