I prefer my 21:9 on desktop, I feel like you'd be stuck with one window on 4:3, but with 16:9 you can make one full window and one smaller one and two full windows on 21:9. 16:9 seems more productive to me.
Desktops do not have the same constraints: you can choose the size (in a much more significant way than with laptops), orientation, and number of displays. I'm happy with my desktop 16:9 display, but mostly because it's a Gigantor Five-Thousand model whose span is taller/wider than my eyes can roll, making the actual aspect ratio kind of irrelevant.
On a laptop space is at a premium, and the ever-narrower displays have in practice been made even worse by modern UI, like the larger Windows taskbar, or that damn ribbon thing in productivity/office suites. On a laptop I often feel like I must scroll every three lines. A (IMO) saner 1.6 or 1.5 ratio would still allow for split screen will giving a better vertical real estate.
I prefer 16:10 on a 15-inch screen but can live with 16:9. However on anything smaller I find a 16:9 ratio too wide. I'm biased in that I spend most of my work time in a shell or text editor where there is a lot of value in vertical space.
The reason I say I'm happy to see a 3:2 screen is that many manufactures cough Lenovo cough say the market has chosen 16:9 or that taller screens aren't widely available enough for them to put into a product.
I too prefer the 21:9 for my desktop. I do notice that you really should mount it higher than I would normally to make feel more comfortable. About 2x what an iMac has for height.
In laptops, I miss the 4:3, and find 3:2 acceptable. I guess I want more square inches of screen. I keep seeing these laptops with 16:9 with a friggin numeric keypad interferes with proper centering.
