Lauren,
My choice would definitely be the IPod Touch! I've used both the older generation IPod Nano and the newer IPod Touch during travels, so have some experience using both.
The Nano is somewhat smaller and easier to carry, and will certainly suffice for music and RS audio tours. However, I find the displays of even the newest generation a bit "limited" for movies or other video content.
The Touch provides a much larger display, and while it certainly doesn't recreate the experience of watching videos on a Laptop or regular TV, it's an improvement over the Nano.
The Touch also provides Wi-Fi capability, which allows Internet use where wireless is available. Using the small screen and Keyboard is not the most ideal solution for E-mail, but it works suprisingly well. However, IMO it would be very awkward to try and update a Blog with that small Keyboard - if you write "wordy" Blogs, it could take a LONG time! A Net Cafe is a much better option (keeping in mind that the Keyboards differ between countries, so that slows down typing to some extent).
The Touch also provides a much greater range of App's, some of which are quite useful for travel (currency converters, expense records, language translators, etc.).
The battery life is not "ideal" on any of the IPod models, however I have now bought an external battery pack that will provide a bit more time for watching movies on long flights.
Happy travels!