Wasn't the Airliner XP one abandoned some time ago?
I have the interim Air Simmer version but it's not fully functional yet and there are some erm... "issues"... with what they have released. If they pull it off, it'll be streets ahead of the other offerings (PMDG-style), in terms of both the FBW and the systems modelling but I'm not holding my breath.
I'm not in a position to compare any of them to the Real Thing, though.