I think it depends on the individual dogs.

My sister's female Sibes want to KILL each other, and I mean that literally.

One of my friends has two male dogs, and they are GOING to kill each other someday, no doubt.

I have five female dogs now, and they all get along well with each other. However, in the past, I have had two females that HATED each other.

I also have five male dogs. They get along well, but my alpha male certainly keeps the other four in line.

In my experience, males do a lot of posturing, strutting, growling, bumping, humping and bluffing. But when it comes right down to it, there is rarely a knock down, drag out fight. And if there is, it is over fairly quickly, when one dog shows submission.

Females, on the other hand, are more likely to quietly co-exist without all the theatrics of pack order ... but when they decide to fight, they FIGHT.

Personally, I prefer one male and one female ... both altered, of course. No same-sex competition and pack-order issues.