I love my Natures Spirit. By far the one that makes me feel safest and is the easiest to use IMO. I also have a Little Giant and have used a hovabator in the past. They're good incubators too and are easy to set up, use and store. The only draw back is the smaller the incubator the more prone it is to temperature fluctuations, so opening it and keeping it in a room where temperatures devlate more than 5 degrees from night to day can be detrimental. The smaller ones also limit you to smaller cup sizes for keeping eggs in.
I made my own, which is quite large, and holds temps well. Made it out of a large styrofoam cooler from Pet co, they get them with fish shipments and save them for people