IC Vienna offers the most elegant Lobby and Bar aera (compared to BUD and PRG). Suite Rooms are good and spacious (I prefer "studio suite"). Classic (club) room is poor. AMB get at least deluxe rooms, usually deluxe corner.
Club* got better in the last months, staff there is average to great (Maximilian ^).
IC BUD: The view is great (only river facing rooms). "JunSuite" rooms are very small, no real suite. Club is one of the best.*
BF: I would rank VIE and BUD above PRG.
At least VIE and BUD allow Club guests to have BF in the main restaurant.
*I don't know, at what time the new (poor) IC Club rules will be executed.