I've done business class in Lufthansa, Swiss and Air New Zealand and the latter were definitely the best: the bed is really flat, the service and food excellent. I don't know whether it's worth spending extra miles on first class when you also have to consider that the connection from BHX on Swiss or Lufthansa will probably be in a cramped regional jet. That be said, Zürich and Munich are well organised for transfers and perhaps Swiss will have the business class installed by the time you travel. But I'd shall out for a limo to LHR and go with New Zealand.