If I could only choose one gender of horse to own, it would be geldings all the way! I have just had the best luck with them. However, I would choose the best individual over the gender. The one with the best temperment, best training and that is the best fit for you.
There was a time I thought I would NEVER own another mare, after buying one that was a real, well, fill in the blank!
But now I own a mare I really love! But still, having to choose between the two, my gelding is a better trail horse. That could also be that he has better training though. Horses are such individuals that it is hard to say how much gender has to do with it, and how much is temperment and training.