Until the catering strike of 2005, I always took BA LHR-HEL. After trying Finnair once on that August, I decided never to go back to BA on that route if possible (and haven't since). While I echo everything Smirnoff said, I feel the difference is far more discernable (in favor of AY). The catering difference is like night and day. In Business on AY, you'll actually get a very good meal accompanied with (real) Champagne and port. AY service (though a bit different than others) has always been nothing short of fantastic. And, I'm still able to use BA's great T1 F lounge (probably one of the best aspects of flying BA intra-Europe anyway).

-FlyerBeek