Booking.com is awful. Anyone can make a listing on Booking.com for places that don't exist. Airbnb at least makes an effort to verify the building is real.
The last trip to Brasil I had problems with AirBnB - both incorrect listings (e.g. wrong location) and listings that weren't actually available.
I've used booking.com around the world and I can't recall any serious problem. When dealing with an issue, AirBnB error flow often sucks and booking is mostly fine.
When AirBnB works out great, you can find some real magic, but when it fails it really sucks.
I've found booking.com is usually more hotel-like and professional (e.g. contactable and reliable).
I still use both but I'm careful to choose depending on perceived risks.
Their hyper aggressive marketing strategy is already telling. Their website randomly pops up when you search and book the flight already. Spanish holiday rental owners don't even advertise anywhere else afraid of booking.com price match policy, but are insolent enough to collect full photo of guests' id document and install cameras inside apartment. Booking is the only place to book holiday rental in Europe and I hate using their service.