The dialogue between Fassbender’s Bobby Sands and Liam Cunningham’s Father Moran in Hunger. Also contains one of my favourite (well, not in an enjoyable way) other scenes, the mopping out of the corridor between the cells in H-Block during the dirty protests. Art house cinema at its best.
For atmosphere and visuals lots of bits of Blade Runner, think I actually prefer where Roy is stalking Deckard through the building to his final speech.
More recently, the church massacre in Kingsman totally blew me away in terms of an action scene – but then I think Matthew Vaughan is the total master of film fighting right now.