My question would be, was it notarized?  If so, the first one that was notarized at the time of signing would be the legal one.  I'm not an attorney, and can't give legal advice, but I would assume if it went to the courts and the notary for each signature was put on the stand, the notary should be be able to ascertain which one was signed and notarized first.  That one would win.  Not necessarily the first one that shows up at the clerk of courts office.  I would be interested on opinions on this one.