As a Jersey born person I would have to say that Guernsey butter is probably more creamy than Jersey butter.

The Jersey cow is probably more well-known than the Guernsey cow and has it's been exported more widely.

To quote the islandwiki

"From 1763, when the States of Jersey first prohibited the importation of any cattle, until 2008 when they finally bowed to pressure from the few remaining breeders to allow cattle semen to be brought in, the famous Jersey breed remained 100 per cent pure in its native island."

And still is in my opinion.

It would probably not be surprising to learn that the import ban was actually in place to prevent the disease that cattle, mainly French cows brought, in a bid to make use of tax advantages afforded to exporters of cows to the United Kingdom via Jersey.

Anyway back to the relevance to BA and this forum. I think that I remember Jersey dairy products being a feature of British Airways menus and drinks offerings in the past so I would not be at all adverse to seeing Guernsey dairy products being available on BA flights despite my natural tendency to inter island rivalry.