A dress problem

Tonight I'm going to a very fancy gala ball, arranged by a student union in Antwerp. I've heard that there will be a chocolate fountain, a cocktail bar, a whiskey bar and even an oyster bar ! So when I say fancy, I mean very fancy!
I can't wait to dress up and choose jewellery and make up and all that stuff, but there comes the problem:

Which dress would I wear?

There are two options, my 'real' prom dress or the new dress I bought.

1. Left dress from H&M (new)

Pro:

-       Goes extremely well with my heart shaped purse (which I drew on the picture for you!)

-       I have lot’s of statement jewellery that look purrfect with it

Con:

-       rather modern, minimal, sober (aka I might be the only one)

-       huge shoe problem and not enough time to buy new ones

-       I can easily wear this dress on other occasions

2. Right dress from Karen Millen (from 2010)

Pro:

-       It’s a tight dress, it won’t fit for ever

-       Chic, perfect for this occasion!

-       Winter print and material (better wear it now then in summer!)

-       It was an expensive dress, it’s a waste to see it just hanging in my closet

Con:

-       I’ve worn it to the two other proms I went (picture problem!!!)

-       Bag problem, only the one I’m wearing on the pic goes well and I don’t like to combine it the same way

So, which one should I pick?