I'm trying to book a trip using my BA 2-for-1 companion pass for this spring and I am wondering why certain cities have tons of availability and why other cities have none? For instance, I don't see anything in J or F for the SEA-LHR or LAX-LHR flights, yet there seems to be plenty of availability from PHL, DEN and IAH. Is this just a case of certain cities being more in demand? Also, would anyone care to comment about the DEN-LHR flight vs. the IAH-LHR flights? The one from DEN uses a 747 and from IAH there's 2 flights, one on a 747 and one on 777. Finally, is it worthwhile to spend the additional 55,000 Avios points to fly F instead of flying J? If it makes any difference, we are a couple flying with a 9 month old lap infant. The taxes/fees seem to be approximately the same. Is the only difference the inflight seat/service/experience? Thank you!