Frankly, I would waffle on wearing seamed stockign to a Formal Ball. I love seamed stocking, don't get me wrong, but these days they are highly charged with erotic overtones, and formal event are generally NOT the place for that.
Hosiery or plain stocking would be best, depending on the length and reveal-factor of your chosen dress.
If your outfit is cut slim enough to show garters or short enough to possibly flash, then I would go the hosiery route. Otherwise, stockings or thigh highs are a good choice.
Just an opinion, of course.