Writing Systems of the World 6, Exercise 3: naming the device

Hungarian "sz": a digraph (two letters, one sound; the Alphabet article lists
Hungarian cs, sz and zs).
German "ü": a diacritic (a mark added to a letter; the Latin script article
lists German ä, ö, ü).
Danish "æ": a ligature (two letters joined as one; the Alphabet article gives
æ in Danish and Icelandic).

Why one over another (my own reasoning, not from a source): a digraph needs
no new characters, so it works on any keyboard or typeface, but it makes the
word longer and can be ambiguous (is "sz" one sound or two?). A diacritic or
ligature keeps one symbol per sound but needs the character to exist in the
fonts and on keyboards. Which wins tends to depend on what the writers and
their technology had available.