I personally say no heat. And as you can see, I live in Minnesota. I don't use heat in the coop (or at least, I haven't so far- if it got down to -30 I may start to think about it) UNLESS I have chicks in the coop with no mama. I've never provided heat for my adult birds so I don't know this first hand, but many other chicken peeps say that heat causes more problems than it solves like condensation in the coop, which can cause frostbite on combs and other exposed areas. It also prevents the chickens from building that thick downy layer underneath that helps to keep them warm, which means that if they go outside or the heat fails they will actually suffer more. The final say for me was when SEVERAL chicken keepers from Alaska said they don't heat- and their coops weren't insulated. If they can do it, the rest of us in the lower 48 can do it.
I do have a heated base under their water, though, so it won't freeze (although this morning was a great reminder to check it each morning anyway- the plug for the base had wiggled loose and their water was frozen solid).