Iphone, 8GB or 16GB??

Hi! I live in Canada and I was wondering if I should get the 8GB Iphone for 199$ or the 16GB for 299$, I have and Ipod nano 2GB and it is fine for me but i kind of want to put longer movies like the titanic on it. And I would also put lots of applications on it. If anyone knows, how many GBs are an application??? Thanks!