DL will charge you the same amount in miles for OW as for RT, so DL should be avoided in this situation. UA and AA change 1/2 miles for OW. To avoid the heavy changes on BA, you might consider using AA miles to fly on IB via Madrid. IB award flights cannot be booked or checked for availabilty on www.aa.com, but you can check the IB schedules for paid travel. Then call AA (fee applies) to book award tickets. Since your plans seem quite flexible, I think that you should be able to find something suitable. Using AA miles to fly AB might also be possible.