Definitely select AA. You can pick MCE for free as a BA Silver, where the seat configuration is the same as BA Y (3-3-3) but with a lot more legroom.
Downsides: The food isn't great, but neither is it on BA. And as already mentioned, only beer and wine are available for free. (Though I thought it was no different on BA in Y? I could be wrong.)
As a BA Silver, T3 might actually be better than T5 for you, as the BA Club lounge in T3 is far less crowded generally than the T5 club lounge (don't bother visiting the Admirals Club).