i currently use infinite flight on my ipad and after a few weeks owning the software am beggining to get bored with the lack of interaction with other aircraft as well as the 2 dimensional runways and no airport buildings.
infinite flight is missing something quite a few bits that will make it as a piece of software that is unbeatable !
as for x plane 9 im still not struck on the application itself as it looks resourse heavy as well as graphicaly mediocre and at £6.99 for the ipad its not cheap ?