For a first time owner I usually suggest male, as they are easier in terms of no egg laying.
If you have previous chameleon experience, its entirely preference.
Some might say Females have smaller space requirements (though I give mine just as much space as a male and they do use it).
Some might say females are less colourful, but I would say they just have different colours than males. I think the subtle browns, oranges, pinks, and blacks with hints of blue etc in a female panther are very attractive. But if you want in-your-face BLUE or GREEN or RED and BLUE, go for a male.