Unfortunately I haven't seen either but I wouldn't be much of a Patty Griffin fan if I didn't add a little "10 Million Miles" vote.
I heard Morrison and Winningham alone were reason enough to see it and it might be Winningham's last musical, you never know.
Truly Patty's music is enchanting and it would be a shame to pass it out. Also as someone mentioned, 10MM is a limited run and well... you never know if you like something before you try it, no matter what others say about it.
"What book of rules says that theatre exists only within some ugly buildings crowded into one square-mile of New York City? Wherever there's magic and make-believe and an audience, there's theatre..."