A good horse is a good horse. Gender doesn't even factor in when I'm horse shopping, I've rode stallions, started w/ mares, then had geldings, now I'm back on a mare (none of it on purpose, just happened that way). I've had horses of either gender that I didn't get along w/, and horses of both genders I was crazy about!
I think my current horse may be my once in a lifetime horse! And she's a mare! She is not moody or difficult (and I have never had a truely hormonal mare, especially while saddled). And she seems like she's in heat alot! But other then being more interested in other horses, if you didn't know her you wouldn't even know.