And what computer do you use? iMac? Macbook? Windows/Linux (HP, DELL, ASUS, ..) ?
At Work, Desktop (Win 10) + 2 BenQ 23".
At Home, Laptop 17", but I gave my external 23" to my wife, so I am on the hunt for a reasonable 23" ish 4K monitor. Any recommendation?
I use the same machine for design and development (I'm abut 50% in each). MacBook Pro 15" and a 27" Cinema Display. For coding specifically, I prefer just the MacBook.
Both laptop and desktop with several screens each (ie more than two).
One screen, but it's a 21:9 curved beauty. On the go I hardly ever code serious stuff, mostly just on codepen since I only have a Chromebook.
A Microsoft Surface Pro 3 tablet with a 27" 2560 x 1440 screen and a 23" 1080p screen.
At work: a laptop and 2 24" screens
At home: 2 24" screens on a gamer tower
I like having a lot of screens, when I travel with my little 13" personal laptop I am always frustrated :)
Have been using multi-monitor for about 15 years now. Sometimes it gets a little silly.
At work right now I use an external display as primary, MacBook Pro as secondary screen (spends 99% of its time showing Terminal). I like the main screen facing me straight on. I don't get how people have the bezels of two monitors right in front of them.
At home I use a few different configurations; but the main machine is a Win10 desktop (mostly ASUS hardware).
Laptop + External 32" screen but not using laptop screen at all (13" Zenbook one)
At work I use Macbook Pro and two additional screen. At home I just updated to LGs 43 inch display and use that as my only screen.

BenQ 24" Monitor with my laptop being shut. I can focus on getting work done on one big screen with more screen real estate for all the code tabs and IDE.
I am using a single MacBook Pro.

Most of my colleagues use at least one monitor in addition to their Macbooks, but I have seldom coded with setups involving multiple monitors. Also, a few years ago, Macbook Air was my primary development machine.
Laptop connected to my 32" TV with 2 vertical windows open on the TV. I need to rearrange my furniture soon so I can get closer to the screen though as I find myself constantly zooming in and out of various web sites.
With my mackbook I use an external screen (while I'm reading a book/doc/blog and coding the examples and exercises) as my macbook has smaller screen and both the book and code editor/terminal don't fit at the same time, but with my other laptop with bigger screen I don't use external screen. So both the 3rd and 4th options are true for me.
iMac with one screen. But the second I can, I'm upgrading to a second (the real question is vertical vs horizontal) and a laptop for coding on the go.
I used to be an iMac + 2 extra screens kind of developer, but I learned that with really good custom keyboard shortcuts, it can be even better than extra screens.
Now I'm happy with 15" laptop screen, and I'm never more than one keyboard shortcut (usually 3 keys pressed at once) away from any app I need :D

I use an MSI laptop and a few extra screens when needed. I don't force myself to use extra screen unless I need them for the given task. I prefer to use as few screens as needed and I don't just place things on a second screen just because I can. One of the reasons I like my MSI is because it has 6 extra heat pipes and 2 amped-up extra fans. I don't game, but I often run the CPU so hard that the laptop would overheat if I didn't have this. With my MSI, I press a hard button on the chassis and it fires up the extra fans, cooling down the machine within 2-3 minutes usually. This occurs because I tend to run 3-4 virtual machines at the same time as well as do crazy string searches and encryption-related search stuff. For this reason, before engaging in that activity, I usually pre-game the fan button so that it never gets hot in the first place. It is loud though, but I can deal with that since I work remote anyway.
This screen usage seems to increase ergonomics, efficiency, and reduce eye/neck strain. The setup works well and I'm still on the fence if I ever want to get a desktop setup again. The main reasoning behind my mobile setup is that I I don't have to worry about doing certain things on the desktop and then forgetting to transfer them to the laptop when I go out and etc...
PS: If anyone is aware of any other brand of laptop that come stock with extra cooling, aside from "gaming" laptops, I'd like to know.
Adi SK
A freelance web and mobile app developer (simplestweb.in) and a proud JavaScript dev, thinking there's nothing wrong with javascript.
A Windows Laptop with 28 inch AOC monitor.