For me it truly depends where I am going, what part of my trip I will be on, and how much time I have. When arriving in Paris (from California) I knew delayed flights were a real possibility, so self check in was my top priority. For the middle part of my trip a washing machine was the top priority, then for my last 4 days, after having a host cancel as my trip was approaching, and having 2 different hosts never respond to my booking request, instant book became the most important feature. I think it's really hard as a guest to wait 24 hours for a host to accept a booking only to never hear from them and have to start the search all over again because my second choice is now gone. That experience gave me a whole new perspective on having instant book turned on.
Given all that, cleanliness is tied for top priority along with the host not having a history of cancelations. Cancelations are surprisingly a real problem in France! I also look for a dedicated rental space, as opposed to somebody's home that they will vacate for a few days while I stay in a pile of all of their clutter. And a private bathroom is crucial. I don't want to be on my way to an appointment and have to wait for somebody taking a shower.
If I'm staying in an entire apartment, I expect the kitchen to be usable and not just stocked with the host's cast off dishes and scratched up pans. Other amenities are all just nice to haves. I want a clean and comfortable bed and bath. I'm not interested in a host providing breakfast or anything else.