Thank you all for your input.
I have Alaska FF miles and for biz class it is pretty much restricted to BA for the London-Seattle leg.
The airports I listed are places I have not been, but are choices that are offered for the trip.
I was wanting to get an idea of what to avoid, unless it was the only choice.
If it does become available one of the direct BA flights would be the ideal choice.
For the trip that did not happen this year, I had booked BA 001, the flight from London City airport , with the stop in Shannon ( clearing US immigration there) and being a 'domestic' arrival at JFK. The Alaska flight home from there was from the same terminal so making the change would have been easy. That option has not yet appeared for next year.
Getting Global Entry is certainly something to consider, once they re-open for business. Now that obligations to family free us for more travel, it probably would be worthwhile
The idea to schedule a 2-3 day layover in NYC had occurred to me, but doing it on one ticket has been a puzzle I have not yet been able to solve