(on my phone, please excuse typos!)
I definitely think the major influence is nurture rather than nature, and also on breed. However, I've noticed a few differences, enough to know which sex I prefer.
I have four dogs, three females and a male. Two altered, two intact (will be spayed at later dates), ages 5 years to around 9 months or so. In my family/dogs I'm around frequently, there's 5 females and 3 males. I'm basing these observations off my own dogs, though I've noticed them in the outside circle too.
My girls are...sharper? More alert/aware? I'm not even sure how to describe it. They're more observant, and two of my girls are much more intense than my male, or the males I've been around. They're more one person dogs, and are more Velcro-y. They want to be near me always, and while they adore physical affection, they want it on their terms. My boy is all about touch, all the time.
My girls are more in tune with people, where as my boy just goes about life in a blissfully happy daze. He's more vocal than the girls, and he'll bark at anything, where the girls are more about actual oddness warranting barking. He barks if I walk outside the fence, they bark if someone pulls up.
My girls can be moody, where my boy is usually even keel.
I really don't see a sex difference with training. I see personality and breed differences. I don't see a difference in who's more likely to be the dominant/boss dog of the group. In my home, Nola is the boss. In my parents', it's a male.