Holmes make a variety of warm and cool mist humidifiers, offering a range of different features. Primarily these are single room models rather than whole house. You can read about the differences elsewhere on this site.
All the current models have antimicrobial protection which will reduce the amount of cleaning you have to do, and help to keep the machine from clogging up with mold.
The range includes different outputs to match different sizes of room. Mainly they are designed for small or medium sized rooms, but the output should be enough for most people. You can always buy multiple units if that turns out not to be the case. If you only have a small room, you could still buy one for a medium sized room and run it on a lower setting. This would mean you have to refill less often.
Some have filters, while others donít. Filters do serve a useful purpose, but they also need to be changed regularly which adds to the cost. If price is an important factor for you then one without filters would be best. It is important to change filters regularly if you have them, as this can effect efficiency.
A very nice feature thatís available on some of their models is a digital humidistat. This is incredibly useful as it enables you to set your desired humidity level. Keeping the room within the optimum range is exactly what you want, and with this digital control the machine takes care of the thinking for you.
Holmes humidifiers use a variety of different technologies, so itís a good idea to familiarize yourself them. You can do this by reading the Different Types Compared page.