Short skirts or long skirts

If you were going to buy a lady an outfit for a nice romantic evening would you buy a short skirt or a long dress?

I would think it would depend on the lady, her preferences, how she would interpret either way and where you are taking her for the evening.

Ooh, it also probably depends on how well you know the person. A short skirt could give the wrong impression if you don't know them very well. So it depends on how well you know them.