Male? Female? Both? Neither? Others?
(I imagine there are times for both expressions, but I'm interested in "general/default" for you.)
I have some reasons of my own, pertaining to my own Aspiration, for wondering.
I've seen people arguing that it tends to express as the gender the magician is most attracted to because that makes for being an easier "lover"; but Bro. Proserpinus (see Black Pearl #6) seems to be a straight or at least bi male, and refers to his Angel mostly as male, owing to the solar-phallic nature of the entity. Crowley's is male, but Crowley's sexuality is complicated.

And certainly Abramelin uses the masculine, but this is medieval times; authority figures tended to be masculine.

And as a final qualifier, obviously not everyone will even perceive so much the "lover" aspect of that relationship, since, of course, every Adept and every Angel are different.
My own perception of my own Angel (of whom I have had the Vision, but not yet KC) has shifted over time and so I find myself curious.
Cheers,
--Shawn