The experience I have had is that I have a gelding and he is fine most of the time but when he gets in a strop (basically he gets very impatient when he is not happy) he barges about, squashes you against stable walls, stands on your feet, bangs the stable door, bangs you with his head, won't stand still...... but is fine to ride even in a strop just don't ask him to stand still....
but my daughters pony which is a mare is so patient, so sweet natured, you wouldn't know she was in the stable, she occasionally whinnies so you don't forget her totally but she is a little saint.... bless....
I think generally, when you find one that you get on well with, then it doesn't matter.
I have 2 mares and do find them to be more opinionated than the boys. If you get in a strop/frustrated with my oldest mare then you are in a losing battle however, if you have her working with you, she is a force to be reckoned with and is fabulous.
The gelding I used to have (and ones I've known) tend to be more easy going but they can have their stroppy moments as well.
If I found the right horse - be it a gelding or a mare - I would buy it.
I love mares and geldings for different reasons, I tend to get on well with temperamental challenging mares, but I however own a gelding, as he is my first horse (actually mine bought and paid for) not just ridden by me, I wanted a good schoolmaster a horse that would take me everywhere, my next one will be younger and less experienced.
Mares rule I always used to think I preferred geldings until I got my mare. She knows what buttons to push, how to wind me up, how to calm me down and generally be amazing. Little mare is much the same