I've conducted an experiment recently... It started about three weekends ago and is finishing this weekend.
The question: Which is harder to handle: boys or girls?
In order to answer this question, I had to have objects to study. My two - one of each - wouldn't suffice. So, three weeks ago I shipped off The Girl and gained a boy. The weekend was filled with all sorts of ruckus. Loud laughter, banging, gun noises, cars crashing, and of course, the Xbox... They stayed up late whispering and playing, and in the morning when they woke up WAY earlier than parental types felt was appropriate, they very quietly went to the living room and located the Xbox again. Any disagreements that arose were swiftly dealt with in a wrestling match and then they were back to playing.
This weekend I shipped off The Boy and gained a girl. The difference was noticeable immediately. There were no gun noises or crashing cars, but there was instant chatter. We've had roll play, bossiness, changing outfits (at least five a day per girl), talk talk talk talk talk, babies, barbies, more chatter... The bedtime was semi-late, and in the morning, when they definitely did wake up MUCH earlier than parental types KNEW was appropriate, there was no such thing as quiet. It was right back to talk talk talk talk talk, roll play, babies, bossing, chatter... even coloring quietly involves chatter with the voices at non-whisper settings. Disagreements were settled by parents threatening to send the extra child home if we can't all get along and then everything was fine.
Experiment finished, I am not sure if the question can be answered as posed. Different? VERY. One group harder than the other? Not really... just depends on the parental types' moods. Do we want guns and crashes and banging or talk talk talk talk talk? :)