I have travelled between MAD & LHR every month for the last 10 years and have, as occasion demanded, swapped between IB & BA. IMHO BA wins hands down every time. Also at MAD the T4S lounge (Sala Velasquez) used by BA (and other non-Schegen airlines) is a haven of peace compared to the Dali lounge which gets awfully busy with IB J's.
I disagree about the IB J food - it really is horrible. Not saying that BA is that much better but I am afriad I prefer BA.
Now that BA MAD has moved to LHR T5 the terrible bussing from gate 24 is no longer with us. ^