I agree that at the age of 40 it is a tough decision - 5 years younger then its still a no brainer.
I do think the net monthly incomes for BA are a little on the low side, especially if you take into account the opportunity for overtime - an extra day can be worth a few hundred quid net at least.
Also nobody here has mentioned the benefits of the BA leave system when combined with bidline. I have one weeks leave at the end of November - through bidding I have blocked my Nov work at the beginning of the month, so I finish on the 15th Nov and return to work on the 7th Dec. I shall be using my free firm ticket to travel to the states in a very nice seat to visit the future in laws for thanksgiving in California. I have a very good mate who got his command this year at Easy who is waiting for his sim check at BA for this exact difference in lifestyle.
For a SH pilot at LHR - I can honestly say that when you compare my roster to the easy equivalent, we definately have a better lifestyle. I don't like early's that much - so I bid for lates, I don't like to work every weekend - so I bid around that aswell, with reasonable success. Before you say "yes but he must be senior" - well I'm not actually in the grand scheme of things. I have been in just over 4 years, but joined towards the front of the last recruitment bulge so shot up the list quicker than average.
I joined BA at 24 - so I am lucky to have a long career ahead - health permitting. I don't think that BA is the be all and end all - but if you talk to any BA pilot, try and find out how many are thinking about leaving to go off to the ME for an early LH command, or to a LC carrier to get an early command - trust me it won't be many if any at all. That should say it all.
Just ask yourself if you genuinely think that you can maintain the 5/4/5/3 roster for 30 years. You may well be able to. I couldn't. Our job can be very routine, and people get stale - myself included, so I am looking forward to the opportunity of moving to a brand new fleet, flying to different places, staying in fantastic hotels, and being paid well to do it. When I have a family in the future - I can then bid back to SH to enjoy many more nights at home. Flexibility is everything as I don't know what I will want and what the missus will want me to do in the future - all I know is that BA provides me with that flexibility as well as providing me with a great quality of life.
Best of luck whatever your decision.