SFO is one of the better airports I've travelled through
As it's not a major hub airport the international terminal is quiet.
Customs and immigration is a breeze in my experience.

BA lounge is nothing special and it's not that big. You used to be able to board straight onto the plane from the lounge, but last two times I flew you had to leave the lounge and board with the other passengers due to "security" checks. Not sure if this still happens or they only do this when there's not enough security resources to have two check points??

Getting a hire car is really easy too now as the skytrain takes you straight from the terminal to the carhire reception