what are some good apps for backing up all iphone data to dropbox?
Due to the sandboxing applied to all application in iOS it is not possible to backup "everything" to Dropbox. Dropbox access must be enabled by the individual application (as a lot of text editors etc. do) or be based on public APIs (like for Photos).

If you are just looking for a way to easily backup everything, iCloud backup would be an option. But you'll need an iPhone to recover any data from there as well.