What route(s) are you flying? AFAIK, there are no routes where SQ A380 and OZ 747 both fly.
Also, OZ only has 747-400, not 747-200.
Agree with others however, F is F, J is not F, so take OZ, assuming the price/routing/schedule is reasonable. (Also, I'm not a huge fan of the SQ cubicles.)