By sweet spot I meant the balance between price and storage. I realize that if you have no trouble affording a 16 GB model, bumping it up to 64GB is the best bang for the buck.
However, if funds are tight, I'd go with a 32GB which would cover most peoples needs.
BTW, I invested in a Hyperdrive case and dropped in a 500GB HD. When away from home I now have access to a lot of movies and files and photos.
HyperDrive iPad Hard Drive