The reality of the situation is that it varies depending upon your origin and destination. If you are simply connecting through LHR, then there's a simple solution: don't Both T3 and T5 are first class dumps and massively overcrowded to boot. For the customer, it's easiest simply to avoid BA unless there's a huge price advantage, which there often is.

But if you live in or wish to visit London, then you have to deal with a London airport. I've never been to Luton on Stanstead, but Gatwick is even worse than Heathrow, so Heathrow's a better choice in reality. If you want to be picky, I'd always choose T2 over the others (I've never been bussed at T2 yet but I guess I've jinxed it now).

Finally ATC delays tend to be built into schedules. It doesn't really matter how long you spend circling or waiting to take off, what matters is whether the airline gets you to your destination when they said they would. BA's not stellar at this, but better than many. If you are worried about that, avoid the US airlines which cancel flights regularly and won't resolve your issues arising from the cancellation.