Ok, then more general: 1, 2, or 3, as long it's Dropbox with local copies :) As there seems to be a trend towards option 3, I'd second this one.

I'd really like to see option 1 or 2. As some other users have already mentioned, being permanently online is only possible for 3G iPads; having only the WiFi version, I would like to keep some files local on the Pad and edit them on the go. As soon as I have online access I can sync the files with Dropbox.
However, having access to Dropbox would be great!!