Which are the key questions one has to ask to decide between Polyglossia and Babel for a XeLaTeX project in 2019?
There has been a similar, more general question in 2012, but the packages have changed a lot in the meantime. Hence I open a new, more specific question.
For LuaLaTeX see: Decide between Polyglossia and Babel for LuaLaTeX in 2019