Honestly, over the years of handling mares, geldings, and stallions, I love both mares and geldings, and don't mind a respectful stud either.
Between mares and geldings, the main difference I have noticed is that mares can be a little more sensitive to most things; not that this is a bad thing, I prefer to know my horse is "alive" than a total dead head, but I think some people just write that off as "it's just a mare thing" and can either make it worse by not backing off of pressure where necessary, or making excuses, and not doing things because the horse is "afraid/reactive". But as far as energy, and ease of training, I think both are pretty equal, as long as you know how to get the results you're looking for. I think in the end, it comes down to training, or lack therof.
"The ideal horseman has the courage of a lion, the patience of a saint, and the hands of a woman..."