I'm very fond of two 4k monitors, one landscape and one portrait. The "main" landscape screen holds what Im focusing on, and the other screen gets documentation, references, unrelated chat, etc. I find this setup very productive.

I have sometimes run a 3rd screen, also landscape, above the primary; but its hard to give it much attention. Good for videos I'm not really watching or background stuff that might catch my attention when it blows up but doesn't demand any notice until then.

I went with a single monitor, a 34" curved ultrawide (3440x1440). Nearly triple (ish), more than dual monitor for sure and I love it. The price difference to go for the 38"(3840x1440?) was nearly triple the cost and was no worth it for me for the extra 400 pixels, though it would have allowed for 3 windows at the size I usually keep them at.

I can not tell you how much I love my 21:9 setup in vertical mode. But also I love to stare at my old 1366x768 with tiny energy use while long sessions of laptoping somewhere out of civilization.