I have a connecting flight from heathrow to frankfurt and then onto miami in the next coming days (both with lufthansa, 1h 15m time between).
My question, is it better to checkin online or at the airport? Is there any difference between the 2 options ie regarding available seats? . If i do check-in online, would i be able to do so for both flights at the same time? And what about luggage, wouldn't that need a tag from the airline at the airport?

Thanks,

Jonathan