There‘s not really much choice in business class product between BER and LHR. Both Lufthansa and BA products are economy seating with a free middle seat. Lufthansa will let you assign a seat for free but without status you will not have the choice of the whole cabin. Food and lounge on that sector is IMHO clearly in BA‘s favour, as would probably be the service on board. Of course, Lufthansa would almost certainly be punctual. BA most likely, not.