If you want a universal format, you have a compressed source tar-ball. Anything else will run into the whims (and on the ground circumstances) of maintainers and admins.
Or cpio. IIRC tar had its own set of issues once you consider old Linux distros or non-Linux systems in general.
Fun story: I once had to exchange data with a Solaris box, and discovered that its tar had no "z" flag. Ended up just exchanging uncompressed tar files because I didn't want to figure out .tar.Z files.
.Z is compress/uncompress, no?
Think so. And it was probably doable, but I realized that my network connection was fast enough that the transfer would be done before I could check.