An issue with sharing large files, is that Dropbox has a limitation on the size of the files you can upload. One solution is win .rar in volumes. Divide the file into a series of .rar each under the size limit. Instructions here:
http://www.addictivetips....ow-to-merge-them-back/ The person on the other side downloads all the rar files, and just opens the first one and they assemble into the original file.
Another solution is mediafire.com which I use for larger files. Its a hard drive system online which you can email people links to access shared files. I got the upgrade and can upload huge files. Nice for backups as well.
As far as the file format goes:
1. cwb for sonar to sonar (as above)
2. everything to wav - export tracks separately. This should be universal, however, some DAW don't read stereo tracks the same way. In this case you need to check box for export stereo as separate tracks.
3. export as omf - some DAW can import this pretty easily. Track info is pretty intact, but no automation.
Always confer with collaborators on what they are using and preferred sample/ bit rates - this is sometimes a hardware restriction.
Write down track notes, and plug in settings or take screen shots - to make sure ideas and info are getting across.
Do a test run - the first try always loses something in translation. Have your collaborator run a quick mix and send you the wav right after importing to make sure they got everything or to figure out what they didn't get.
Good luck!