IF you're talking about a 'pseudo' tablet PC (or phone) where 8GB~32GB is ALL the storage then minimum of 16GB and IMO better the 32GB
. If you like Movies then figure ~1.5GB per full length movie, 1-2GB+ for Apps, and XGB for your Music. My daughter has the iPhone 4S 64GB and it's full! I on the other hand am using 12GB of my 16GB capacity on my iPhone.
So it all depends on YOU