Marriott cannot be converted to AA, so that is out. The best conversion rate is to AS and BA, both of which can be used to redeem on QF. Other choices are DL (pretty good J LAX-SYD) and HA (flies older J HNL-SYD but might suit if wanting to combine with a vacation in Hawaii). For completeness can also convert to LAN (and lots of other airlines). Availability severely dictates your choices if not having tremendous date flexibility. AS is probably the best redemption but choices are complicated except converting to QFF is a bad idea.