I like them both and think you look lovely in the first one. The second is beautiful as well and I'm sure you'd be amazing in it.
But, possibly the fact that the first one is sort of an heirloom type dress will make it more *special* and appropriate for graduation?? I'm sure your God Mother would feel wonderful that you wanted to wear her dress.
Only you know what type of dress is normal for your high school dance- all high schools are different. Choose what you like and what makes you feel special. You'll remember this day always.