@Nuno Lots of good and bad experiences. Airlines are usually fine, I've used Ryanair, Iberia, SAS, British Airways, KLM, Finnair... My only remarkably bad experience is with KLM.
Accessibility for booking: varies a lot, and changes all the time. It's usually possible but sometimes fiddly to get tickets.
Airports: overall good, though a lot of airports insist on me using a wheelchair because it's more comfortable for the person assisting me. Amsterdam was interesting in this regard, they insisted on a wheelchair but they also gave a lot of useful assistance, including getting me to a hotel as I had to stay a night due to a missed connection, and back to the airport on the next day. Lost track of me at Barcelona once and if I hadn't used my cane to find an information point and asked for help I would have missed the flight. Some airports are pretty well organised, some are more chaotic but things still get done. Dublin for example seemed like short of a crisis all the time but things got sorted anyway.