We have flown into/out of SFO/IAD/DEN (S Francisco/Washington Dulles/Denver) in the last 5 years and have had no trouble at all with Customs and Immigration Staff - they have generally been polite/helpful and sometimes with a quiet sense of humour (although a fair number are fairly serious in demeanor).
I guess it does depend on which airport you fly into but the 3 above were fine,having said all that - much of your 'arrival' experience will always have a percentage of luck involved
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As I posted previously - flying through DUB may well have advantages for some people but there will always have a slight risk of problems involved with the extra stop/leg and the overall journey time is never going to be faster than non stop.
Personally I much prefer do do a non stop and just get the pond crossing out of the way,because we live north of the border (Scotland) we do sometimes travel a long way to get a decent flight price - the trips I mentioned above were variously flown from Manchester/Edinburgh and LGW - but if we had to travel (say) all the way down to Gatport Airwick for a flight - we would always fit in at least few extra days and visit family and/or (say) Duxford or similar.
We did a road trip round some of the eastern/north eastern states last year (from IAD) and the only place we came across an a55hole border officer was when we walked across the Rainbow Bridge at Niagara Falls, when we made the mistake of asking him some advice as we left the US side - the guy was obviously a bit of a psycho,when we returned later after having had a lovely couple of hours in canada all the other border officers seemed friendly and fairly laid back.