Intact male dogs will roam, be willful and some of them can be a handful. I have a male doberman and he is inact as of right now, and he is a pain in my butt at times.
If he smells a female near he won't listen, just mark the ground, trees, and look for her. God forbid he finds her, if he was a person he'd be in jail for rape.
Then again, depending on the breed you can have a male dog that is pretty mellow, however ALL intact males if they smell a female going into heat or already in heat they will become pig-headed. It's just hormones.
Females some breeds like dobermans and mastiffs when they are in heat they get territorial, and fight even with other females.
My rule of thumb is if you aren't a qualified, and conscious breeder with the only priority of perfecting the breed and not making cash then get your pet spayed or neutered.
and to dispel some of the myths, unlike what someone said above a female who has been spayed does not become lazy, and fat. The only way she would was if the dog didn't get exercise and a proper diet, just like people. The same goes for male dogs, it DOES NOT inhibit them from being good guard dogs or make them fat. It does take away from their facial muscles you can see that in the jaw-line of an intact male and a neutered one..BUT still a wonderful dog either way.
If you have children I would suggest a female, especially if it is a big dog, males do mature slower (like human males no offense) females learn how play with children carefully, and of course they treat them like puppies, become very attached to them. (Our 1st doberman female was like that, the males attached as well but never to the degree that she was, but that doesn't mean the males wouldn't have laid down their lives for us)
Hope you choose well in your quest for a good and loving pet...
Choose the breed first, THEN the gender
Owned Dobe's for years along with several small breeds....