In order of importance:
2) Convenience - I live in West London so Heathrow works for me. Most travel now is to North America (NY and SFO) so the BA schedules work best for me too. Colleagues that fly to the Far East haven't flown BA for years though.
3) Frequent flyer programme - although I have dipped in and out of BMI (and got some great flights) the BA programme definitely helps push my business to BA. I get most use out of MFU WTP to CW which is great value (when you can get it).
5) I recognise that for some people BA is something of a 'marmite' airline (you either love it or hate it). Sometimes they have an off day, but on the whole I like the service. As others have said, when you are returning from some far flung hole, you do get that warm fuzzy feeling when you step aboard.
8) and 9) A T5 fan here despite having been right royally mucked about on opening day (should have known better really). Biggest hang up is still security which isn't really BA's fault. The lounges are pretty good both at T5 and T7 JFK.
12) Comfortable seats - I know the opposition is catching up but for years this was a clincher when you considered some of the rubbish seating provided by the opposition. Lucky that most of my flying is in J but if it was WTP/PE then BA might lose out against VS or Qantas. BA needs to step up in a number of ways there. Can't comment on steerage.
6) Unexplained love....or 6)a Nostalgia with a bit of 4) British Patriot - my father spent his life living and working overseas and wherever we lived BOAC/BA was there to take us back to the UK for school/university and then back home for the holidays. Have tried to stick with BA as far as possible ever since. Glad to 'fly the flag' even though recent debacles don't always make that easy and the relentless cut-backs do make one nostalgic for the (recent) good times. Yes, we do notice the cut backs!
10) Food and Wine - low down on the list as BA doesn't stand out on the food front. BA is above average for wine though (on board and in the LHR lounges). As someone who enjoys a 'cold refreshment' this is a not insignificant scorer. Please keep it up!
as 7) and 11) are not particularly significant for me (I do appreciate the staff input here but not sure it helps me make a choice) that leaves
1) Price - for work, unless BA is out by miles, we usually get BA to North America as the US airlines are just not contenders. Our default option is VS but I still pick BA if they are within GBP 200 or so which is often the case as BA/VS seem to track eachother on price. Would I choose VS because they are GBP50 cheaper - no I would not. To the Middle East/Far East Emirates seem to be winning on cost.
For leisure, usually try to use MFU (or redemptions) off a sale base fare for long haul, but if the price isn't right we just don't bother. We've had quite a few good deals over the years but without the MFUs we probably wouldn't pay the full fare in CW or WTP. I won't fly back of the bus on anything over 4 hours.