I would consider what it is what you want from a scheme; although getting status may be easier with QF/BA , you could get a better return on miles earned vs redeemed elsewhere ( such as AA )
Qantas Status credits are based on distance flown and class of travel utilised and is listed at
http://www.qantas.com.au/fflyer/dyn/...status-credits. A Simple TIP-LHR-SYD would earn 80+360 = 440SCs . If booked TIP-SIN-SYD would earn 80+ 240 + 180 = 500 . If booked TIP-BKK-SYD 80 + 210 + 180 = 470
Using BA does have a big drawback of having to backtrack to London ; travel 3 hours and be further away from the destination than from where you started. There are options to Australia from there which are more direct
Dave