I think you have to come to grips with the answers to several questions ...
- What is your expected full timing lifestyle - out and about most days (sightseeing, sports) or spending a good amount of time indoors?
- Why are you fulltiming?
- What is your fulltiming footprint - lots of hobby/recreation stuff or a minimalist footprint?
- How active are you in the Airstream community? Are rallies, AS parks or caravans a significant part of your plans?
- What is your financial comfort level? Large, high quality class A's are expensive, as is the maintenance and repair. And large class A's are very complex with reliability likely worse than most Airstreams.
- Where do you see yourself camping - large sites with 50A service or smaller/older parks?
a large diesel pusher class A has a lot more interior room and storage space. That is traded off against purchase price, operating costs, potential problems requiring professional service, lack of the Airstream community and a more mobile home/apartment feel rather than the Airstream aircraft/yacht feel (this may be a bug or feature).
There is also the consideration that many large coaches have residential appliances that require running the on-board generator for boondocking - this might be a problem is sites are generator restricted or you just don't like the continuous noise (as well as resupplying fuel).
The crux of it is "full timing" means very different things to different people