For us, male/female or female/female works best. Chester doesn’t tolerate males at all. He gets along wonderfully with Millie, but barely tolerates Aneko. Millie and Aneko sleep next to each other and have never had “words”. So I think it really depends much more on the dogs, rather than the sexes involved.

My SIL’s female has picked fights with both Chester and Aneko. Millie basically gets along with everyone, lol.