I've done very well with short stories and novels sent back and forth as attachments, saved in the earliest version of MS Word either of us has. (More and more often, it's mine, Word2003.) While I can convert later versions of Word, it's a PIA, whereas the author saving his/her work to a 'lower' version of Word is a matter of seconds.
My very favorite way to critique or beta remains on paper, but I've only done that for an AW person once. Line edits are certainly easier for me on paper.
Maryn, thinking whatever works for any two people is cool