Short or Long Prom Dress, Which One?

I will attend the party a few days later, but I haven’t chosen the prom dress for the party. Because I have some problems. I want to wear long prom dress at party and also pick from online shop named luckbridal. The prom dress is so beautiful and the fabric is chiffon. Beadings embellish on the bodice and shoulder. It is so sparking.

http://www.luckbridal.com/stunning-beaded-evening-dress-v-neck-chiffon-prom-gown-1399.html

But my sister didn’t agree with me. She thought the long prom dress is too conservative for me and don’t suit my age. She chooses another prom gown for me. The dress is short to the knee and halter to the neck. Furthermore, the shoulder is naked. But this prom dress will let me very young while the long prom dress is mature.

http://www.luckbridal.com/enticing-white-halter-prom-dress-organza-prom-gown-1404.html

 

In addition, I will graduate from the university next year. Which one should I choose? I need some opinions.
Oh, I have limited time to consider it.