WELL. I dunno which one you should pick, but which one makes you feel more BEAUTIFUL. Which one could you spend a whole night in? I mean, if you wear flats with a maxi, it doesn't really matter as you can't see your legs anyway! And you're tall, so can pull it off. And if you wanted a long dress...
BUT at the same time, you don't HAVE to wear a long dress, so if you prefer the other, just go for it! I think you know which you're going to pick though, as you're making excuses for the maxi, and you're not for the short one :P