Further, while I've only gone through CBP in four countries, I will say that the US is the only one that qualifies as nightmare for me. Walt was talking about paperwork, my experience is with attitude. The US is unique in their CBP people having a chip on their shoulder and acting like asses. As I have written about before, I have been threatened with $5,000 fines three times entering the US. In all three cases the mistake was on the part of the CBP. In all three cases their treatment of me and my pax was a nightmare. In none of them did they apologize. They actually seemed even more ****y once it became evident that they were the ones in error.
Any good checklist for entering the US will suggest you write down the name of the officer you speak with when you call to confirm your arrival. I can't emphasize this strongly enough.
Anyone who does this regularly will be have "shopped" the various AOEs and can tell you which ones they prefer. I lately use McAllen, TX almost exclusively because I have never had a single problem there and, beyond that, the staff is almost uniformly friendly and pleasant to talk to while they (efficiently) do their jobs.