Your body needs the energy to properly digest food. So to get the most out of the nutrients you consume and your workout, eat before exercising or 30 mins after fruit, two hours after veggies, three hours after grains four hours after meats and poultry.
So it's not a matter of value, it's a matter of what you need it to hold. And a matter of affordability. The movies will be the biggest space hog. So if you only put the movie you want to watch next on the iPod touch, so one (or two) movies at any given time, you will have more than enough space with either 16 or 32 GB. People watch movies once (twice if it's really good); they do not watch a movie over and over again like listening to songs.
Quick Answer. A 4 gigabyte MP3 player can hold approximately 1,000 songs. This estimation assumes that the songs average 3 minutes and 30 seconds and are encoded in MP3 format at 128 Kbps.