I’ve taught for 7 years in a military prep school using chalkboards. I love them. We have the students clean them daily, so there is good contrast between the chalk and the board. There is no problem erasing old material. Chalk is plentiful and cheap. The boards never wear out.
However…
Chalk dust ends up covering every object and surface in the front third of the classroom. Also, I end up covered in chalk dust after every lecture.
I do have a white board in my office. I far prefer this to the chalkboard, since the chalk dust in my office would drive me nuts.
However…
I never use it, because some drawings my 4-year old put on it that I didn’t want to erase are now permanently bonded to the white board. In fact, all white boards that I have used seem to require a great deal of maintenance (or replacement) to keep them erasing properly.
In short, chalkboards are messy, but they always work. White boards are more modern and less messy, but don’t always work.