X bracing versus parallel
The two most common bracing types used on archtop guitars are the parallel and the X bracing. The parallel bracing is by far used most. Maybe because it more easy to make and because it has a more direct link to the violin family which should be considered as a important example for the first archtop guitars.
I think the reason that brands like D' Angelico and Gibson started to use X brace instead of parallel is structural and sound. X braced tops are made a bit thicker in the bridge area than parallal braced tops because the X will give less stiffness in the bridge area but much more overall stiffness over the entire top surface. X braced archtops give less projection than parallel braced tops sound mellow and warm whil the parallel braced tops really cut.
These days most luthiers of fine archtop guiars use the X bracing as a standard. The picture shows a nice mariage from my Tonemaster model with an Excalibur headstock. Very blond and very X braced.