Mmm... I work for the RAF, and I find it difficult to choose my favourite aircraft!
Airliner, Concorde is beautiful but I have a soft spot for the DH Comet. (Damn, the VC10 is in there too!)
Vintage military, any late marque Spitfire, the bigger the Griffon engine the better! Favourite is Mk XIV.
Mossie is there too, but the old Stringbag gets a look in too.
Modern military, The Typhoon FGRA 4, the most manoeuvreable and stunning modern jet fighter I have seen fly, its also the only one I have seen go supersonic during my tour in the Falklands. It has Lightning performance with the load carrying capability of a bomber- the only aircraft in the world that can carry out a spectacular air show aerobatics display with a full fuel and weapon load! Very impressive!