If I had my way, all I'd ever ride would be mares.
When people have issues with a mare they generally just whine and complain about "how she's just in heat." My experience is that the mare has just been allowed to get away with bad behaviour and/or that the person in question is just incompetent. When mares are trained and treated correctly they are just as good as a well trained gelding. It's like saying that when a woman's mad "it's just because she's on her period." It's an excuse and one I don't like hearing. YOU are the person, THEY are the horse, end of story. I find that mares are more opionated, as others have said, but I also think they're also more willing to THINK than some geldings (not all, obviously.) IMO, a good mare trumps a good gelding any day of the week. There was a reason that the Bedouins treasured their mares above all their other horses. And I, also, love mares.
"Always be yourself. Unless you can be a unicorn. Then, always be a unicorn."