I buy the horse not the gender, and have owned both. If I ever get ready for another horse I will not be picking based on gender.
That said I currently own a mare, the rest of the family has geldings (three of them), and guess who's the best behaved? My girl of course.
I once heard someone say 'you'll prefer geldings, til you get a really good mare', and I can for sure believe that!
Geldings aren't moody, really? They are in my experience! As far as riding it's a training issue, but we can't really control what they do in the pasture. All our geldings (well they're not mine) currently need some work on the ground. I can tie either of our mares (my mare and our pony mare) near or next to any other horse we own (or pasture them w/ anyone else w/out issue), but we have to be careful w/ the geldings, especially w/ my dad's horse (not that he's the trouble maker, just they are worse when he's there) who doesn't live w/ the other geldings (my mare doesn't either). Magic is very possessive of mares he considers 'his'. He and my sister's horse Wizard lived fine w/ each other, then we put our pony (mare) in w/ them, and suddenly the fight was on, not w/ Genie (the pony), but the two geldings, til poor Wizard was shunned and not allowed near the other two, and Genie was not enjoying the attention. Things have calmed down, Magic still likes to stay stuck up Genie's butt, but they aren't fighting anymore. Currently Magic does not like Sockett (dad's horse) because he gets alittle to close to Gypsy (my mare).
It's not a maturity thing either, guess who the youngest horse is? My girl! And I'd guess the pony is around her age to.
Now for the training issues, they are all wonderful boys and easy to deal w/, but if they were mine I'd be working their butts off to resolve any training issues, and they'd be much better behaved. But I still can't control how they behave on their own time.
Just have to stand up for my very non moody mare (and most the mare's we've had were not moody, and those that were were moody in or out of heat).
The funny thing, for a long time Magic was the bottom horse, and I always considered him the most gelding gelding I knew! And now he's the biggest trouble maker! I actually blame this on the fact that all our horses are on the submissive side and someone has to step up and be the boss, Magic thinks it should be him, and he just doesn't have the right temperment for it.
Again that said, I wouldn't trade my mare for any gelding in the World, but if I go horse shopping I won't limit myself to one gender.