Here's a seating chart for Business Class on a weekday flight on American Airlines from JFK to SFO.
Also note that all the middle seats are taken, except for in the first row. These people are smart, assuming they don't want to look out the window. They can get up at any time without having to step over the other guy. And the other guy doesn't have to step over them. Very rational way to travel.
Me, I'm angling for the window seat, without anyone next to me, so I can spread out. However if I have to choose betw a window and aisle seat, assuming both are taken, I'll go for the aisle seat. I like to come and go as I please. I get restless and like to walk around esp on a 5-plus hour flight (and it's raining and windy in the Bay Area so it's likely there will be some delays).