Do you have any kinds you are considering? You need to consider what you're willing to pay. Honestly, the foam ones you could probably make yourself with a little know how. I've used Little Giant in the past, but due to user error, had a bad hatch. Otherwise, I've just had my hens do it the old fashioned way!
brinsea eco 20 is what I just bought,
I did a lot of research bought a little giant had so many issues with keeping the temps right and hard work turning the eggs that I could not stand it and got rid of it and bought a brinsea and put a load of turkey eggs in and so far I have candled twice and everyone but 1 shows life moving around in it and they are due to hatch in less then a week.. oh and never had to worry about the temps as it came already perfectly presetted and turning is a breeze just turn the machine 3 times a day not each egg.. nice..