In the wild, a female rabbit is always pregnant or a mother. When she isn't bred, she can get grumpy, mean and antisocial. If she isn't spayed or bred, she will generally live her life somewhat depressed. Of course, there are the exceptions. Some does would rather die then become a mother. Some does aren't good at motherhood at all, and they know it.
When you spay your female, she lives a life more of happiness and relief then having these I-need-to-be-a-mommy hormones always aching her. It would make you grumpy, too, wouldn't it?
In the wild, a buck is always breeding. I'm sure not a day goes by in the rabbit world that a buck doesn't breed a doe.
Most people will tell you that a buck makes a better pet because his hormones don't change his attitude. So instead of becoming antisocial, mean and grumpy, he'll stay sweet, adorable and lovable.
But bucks have hormones too. And maybe they don't show their unhappiness in the way that does do, but it's still there. Sometimes, once a buck reaches adulthood, he will spray his urine to mark his territory and let the does know that he's around and ready to mate. Sometimes he'll preform the "mating motions" on anything he can get his paws on, including your foot or a stuffed animal.
Does and bucks each have their own drawbacks. But when either is spayed or neutered, they generally live a healthier, happier, care-free life where they can be the pet rabbit you've always wanted.