I'm actually taking these flights as part of a oneworld ticket...so there wouldn't be any difference in base fares, right ?

so...
(1) in general I should take AA # instead of QF # ?
(2) If I'm flying in May - should I take QF or BA # ?
(3) How about CX vs. AA ? e.g. SFO-HKG...should I take AA # or CX # ?

and, in general...what if I issue a segment with a certain airline, and then decide to switch to another airline ? would they ask me for the difference in fuel surcharge / tax ? or give me refund ? (probably no?)

or if I issue the segment as open carrier (can I do it in a oneworld ticket?) - what airline's surcharge/taxes would they use for that segment ?

thanks.