BA used to be quite good (100% bonus for Silvers from late 2010 plus Silvers already have lounges access), but they are about to start 'enhancing' the program, so I will stick to *A for now.
Have you looked at the changes? The enhancements - with the exception on Euro thresholds and some elements of the partner award chart - are pretty positive. How many programmes recently have reduced the miles needed for key destinations e.g. NYC?