Google Docs have a nice change-tracking and commenting system and next to no learning curve. The downsides are the formatting, which is rather unpredictable for complex-ish documents (figures are always a mess), and citations.
Overleaf helps get formatting and bibliography out of the way, but everybody must know at least some LaTeX, and you have to come up with your own comment-and-response system to keep track of what's going on. There is something baked in, but it is not satisfactory. On the other hand, it is very easy to just comment out stuff that is no longer needed in the main text but may still be useful or just serves as easy-to-see revision history.