It depends on how much you want to spend, what you're hatching, and how many eggs you're willing to lose. A Hovabator will do OK with fresh chicken eggs of your own. Forget it for turkey eggs - you can't raise the humidity enough.
I've no experience with ducks, but I suspect they need high humidity as well.
If you want no fuss, no muss, and amazing hatch rates, I would recommend a
Brinsea Octagon 20 with the humidity pump. I found one used on Craig's list by google-ing the name and reading through multiple pages - you can find Craig's list postings from other areas that way if you're willing to scan through many search result pages.
You put in the eggs (don't need any special racks) from Quail to Turkey, set the temp (or use the default), set the humidity, and except for filling the humidity pump container, forget it until lockdown time. Then take out the egg dividers, reset your temp and humidity (if you need to for the type of eggs you're hatching) and wait for them to hatch! It's a bit crowded the first 24, but if it gets too bad you can quickly take off the top, grab the hatched ones and put them in the brooder, and the incubator will be back up to temp and humidity in a matter of a minute or two.
I work 56 a week, with crazy hours, and the
Brinsea has been a great thing for me, as I can go off to work and know everything will be fine.