Things to consider:
How many eggs do you want to hatch at a time?
Are looking for just a few to show your kids the wonder of seeing a new born chick emerg from its shell? Or are you going into full poultry production? If you need to hatch just a few, GQF's Chick-Bator is an option you can try. It is very economical and compact but it's simplicity also makes it not an ideal environment for hacthing eggs. Many customer reviews show that a 30-50% hatch rate is about what you can expect. Another option to consider is IncubatorWarehouse.com's IncuCube (tm), a small, compact incubator that will be launched in early March. It will hold a dozen chicken eggs, about 6-8 goose eggs and 18-24 quail eggs. See our Company News page for updates on this option.
Two very common incubator options on the market today are the Little Giant and the Hova Bator egg incubators. These each hold about 40 chicken eggs and 120 quail eggs if you use the automatic egg turners. They will hold more if you are willing to turn the eggs by hand. They are relatively economical and will last for many years if properly taken care of.
If you to hatch more than 50 eggs at a time, you can use more than one table-top incubator or you can choose to invest in a cabinet style incubator. These can range from a hundred egg capacity all the way up to several thousand eggs. And the price will go up accordinlgy.
How large are your eggs?
Are you hatching humming birds, quail, grouse, chicken, duck, goose, turkey, emu, ostrich? This will make a difference in which incubator you select. The Little Giant will do everthing just fine up to a duck if you use the automatic turner. If will work for goose eggs if you DON'T use the turner. The Hova Bator has a higher ceiling so you can purchase goose racks for your automatic turner and it works just fine. If you want to hatch something larger than a goose, you better look at something like the IncuCube. It has a nice cube shape which makes it better for larger eggs, though you will be limited in the number you can hatch.
Where will the incubator be located?
If it will be in a place where there will not be very many people who are trying to see what it happening inside, then you don't need to be as concerned about the size of the viewing windows. If you are using this in a school class room where many eyes will want to see the eggs peeping, larger viewing windows will be a plus.
How often will you use it?
Will this be a one-time thing? Are you are going into steady production? The HovaBator has a nice plastic sanitation liner that allows you to easily clean the bottom of the incubator and immediately start another hatch. The Little Giant incubator does not have the liner.
How much time do you have to be involved (do you need an automatic turner or not)?
The question of whether to get an automatic egg turner or not comes up a lot. There is no question that eggs have to be turned regularly. The question is, do you want to do it by hand or have an automatic turner do it for you. Well, how much time do you have everyday? How forgetful are you? :) How careful can you be with handleing eggs? Some people like the interaction and closeness they feel when turning the eggs everyday. Others simply don't have the time or won't be around often enough each day. Keep these things in mind as you make a descision. We have found that the consistancy and gentleness of the automatic turner makes it an investment that is well worth it!
Other things to consider (more info coming soon):
What can your budget afford?
How much space do you have to store your incubator when not in use?
Who will want to watch the eggs hatch? Just you? Your children? A whole room full of school children?
Other things to consider: Clean up (sanitary liner), reliability, durability, etc.