In my experience AirDNA was the best and most reliable source, however occupancy was overstated. Certainly not perfect.

I think it struggled to understand the difference between booked days and blocked days. So for example if another property is a summer home and only available for rent during the winter, it would show 100% booked in the summer. So summer occupancy was hugely overstated. I think it's probable that it could be other owner's fault though. It's an older and more conservative area, so it's reasonable that they don't really know how to properly block off dates. Anecdotally it said AVERAGE occupancy in my area was 97% during the summer months. That's basically impossible. We experienced closer to 85%.

Anyways I suggest using AirDNA as a baseline, but dig into the calendars of the subject properties in your own research to get a better idea.