A two-hour movie runs 1.0-1.5 GB. Apps there's no way to estimate, as they can range from very tiny to very large (one game just announced is reported to be over 1GB).
As the others have said, unless you're on a very tight budget, get the larger capacity. You may not use it, but if you do indeed want to have around 10 movies in your iPhone, it would be quite easy to run out of space in a 16GB iPhone.
Regards.