What dress should I wear for my highschool graduation tomorrow?

The dress code for my highschool graduation is the standard cap and gown with girls wearing dresses/skirts and dress shoes. I'm trying to decide what to wear and wanted some outside opinions. I just bought this really cute dress so I'm wondering. I have long brown hair that I'm planning to wear down, and a light complexion except for my face which is slight reddish and I have a slight farmer's tan. (I live on a farm.)

1st choice; A cute yellow and green flowered dress. It's not silk or anything fancy. It's made very simply, has short sleeves, and goes down to my knees. My sister, and aunt both wanted it, but Mom had already gotten it for me. I'm debating about giving it to my sister because she seemed to like a lot more than I do. My grandmother thinks that I should wear this dress.

2nd choice; A sleeveless green layered, and purple flowered dress that goes down below my knees. It's a bit heavier in material, but it looks more dressy than the first dress. It might also be very slightly big on me.

3rd choice; My last choices are all pretty much white with lots of bright random like color patterns. One of them has only one sleeve.

Which do you think?