Still air incubators are more like having the eggs under a hen. The air on top of the eggs is warmer than on the bottom, and turning the eggs ensures that they will be warmed evenly. You need the temperature in a still air incubator a little higher than a circulated air one, so that the bottoms of the eggs are not too cold. Circulated air incubators have small fans that move the warm air around the eggs evenly. Some types of birds do better in a still air incubator, but chickens do fine in either type. I would pick your first incubator based on how much time you have available to spend on it. If you are not ready to babysit your eggs all day and all night for nearly a month, go with a model with an automatic turner. Look for models that are known to hold their temperature well, so that you will be less likely to need to adjust your temperature during you hatch. If you are not familiar with how the incubator's temperature dial behaves when you adjust it, you could get some big shifts in temperature. I would suggest getting your incubator as far in advance of the hatch a long as possible, so you can start it up, have it running for a while, and understand how it behaves - every brand runs slightly differently. I'm still calibrating one of my incubators, while the other is running exactly at temperature. Before you know it, you'll be hooked on incubating like the rest of us!
