If you find you're getting identical flight times on BA and QF "flights", you may actually be looking at the same flight. BA and QF codeshare on every flight from LHR to Australia via SIN and BKK. Make sure you know whose aircraft it will actually be, if that matters to you.

For the aircraft alone, I marginally prefer QF to BA in economy. I happen to fit into the QF seat better, but that's probably very personal to me. I personally think BA cabin crew and service have the edge on QF, although QF has made some recent enhancements - like the mid-flight snack pouch which is totally useless to me because I don't want it during the flight but I'm not supposed to carry it off.

If it matters to you, frequent flyer points earn is governed by the code you're booked under. A QF flight number earns as a QF flight even if it's actually operated by BA, and vice versa.

What you earn also depends on which scheme you're trying to earn in. If you are a member of QF's, you'll basically earn 100% of flown miles as points for discount economy fares on all QF and BA flights, and 50% status credits if you take a full economy fare as the benchmark.