BA 9/10 is the BA flight, QF 1/2 is the QF flight. Both of these are 747-400s.

The best seats are centre row aisle seats. At worst, you'll have the person next to you to contend with for "pit stops". If you're lucky, there might only be 1 or 2 people in the row, so you won't have to contend with the dreaded "excuse me" while you're (trying to be!) asleep.

I've done both, and you could pretty well flip a coin. I would ask your TA which flight has the lightest loads, and/or allow seat pre-allocation, and take that one. I think the QF seat is marginally better, but that's my 5'9" 72 kg frame...

Of course, if miles/status credits are an issue, you have another issue to take into account.

Finally, seriously consider World Traveller Plus (WT+), BA's "premium economy" product. WT+ is worth EVERY cent.