This is one of the reasons that Apple switching to 16:9 on the iMacs did not turn me off completely, they made them larger in order to retain the same (or better for the 27) height as the earlier 16:10 models.I have a 32-inch 4K display which I feel is very big but it also provides an unparalleled level of productivity (but it required some getting used to due to its size). I use it at 125% scale.
I also have a 27-inch display with a 2560x1440 resolution which is great for productivity as well.
I have a 15.6-inch laptop with a 3840x2160 resolution which I use scaled to 150% which provides great productivity for a laptop. I prefer a 16:9 screen on these larger displays as it is better for side-by-side multitasking. I felt the screen of my 15.4-inch MacBook Pro was too tall, and more suitable for performing one task at a time (not my kind of use).
The laptop which I use on a daily basis has a 1920x1080 14-inch screen, which is good and I think the smallest bearable size for side-by-side multitasking.
And I have two MacBooks with a 13.3-inch retina display and 2560. They are fine, but I think that the extra width of the 16:9 14-inch provides more room for multitasking (while keeping the same height as the 16:10 13.3-inch).
Interesting to see someone else using those sizes, I actually overall prefer displays in that size too. 24" is really ideal, but 27" is about my limit for 16:9 due to width.For desktops, I usually like something in the 20”-23” range. At home, my Mac Pro has a 23” Cinema Display and a 23” Dell attaches to it. In my classroom, I have a 2010 21” iMac with a 20” Cinema Display on it. I really wouldn’t want much bigger than that, especially in the classroom. I need room on my desk for other stuff, and I need to be able to see over the screen to see the kiddos
As far as laptops go, the smaller the better. I get laptops to be portable, and have always used the smallest ones I could get my hands on. A 12” PowerBook served me well all through college, and was replaced by a 13” Air, which in turn was replaced by an 11” Air. I use a 13” white MacBook for school, as it’s cheap and expandable, while my home laptop is a 2015 11” Air. If I need a bigger screen, I can just plug one in.