Bench. We only have one little one, and there will be no more. Part of the reason for the Acadia in the first place is how hard it is getting for my wife to get the girl into the Jeep. The Acadia will help mom help the girl step into the back, and then the little girl can scramble onto the center position and then into her chair.
But secondly, it was bought for more comfort on trips. My inlaws live 120 miles away, and my parents (who are local) have a weekend cabin 200 miles away, and we plan on visiting both more often. I almost always drive, because I am not comfortable in any other seat, but would like to be able sit in the back with my girl and watch movies (ok, I will probably use a laptop instead of watching Cinderella for the 50th time)--- the bench is just more comfortable to me -- I can lean sideways, I have the big armrest with cupholder.
Plus I am guessing (but it is not necessary)- I can do the smartslide on the 40% chair to still get to the back even while the car is in motion.
We won't have the 3rd row even up very often, it will mostly be used for cargo-- in the same way the 3rd row was very rarely used in my parents 78 Custom Cruiser when I was a kid. It was a lot more handy to have 3 in the back seat before the 1st person went to that 3rd row (although sometimes it was fun to be back there, going backwards.)