DAProg's is stackable and can be fitted next to each other for Cin and Cout. Very nice and slick as always from DAProgs.
SeventhSandwich's 4-bit adder:
8 x 8 x 9 = 576 1x1f in volume
DAProgs' 4-bit adder:
6 x 6 x 17 = 612 1x1f in volume
By pure volume alone mine is still smallest :)