Slackware on my desktop, Mint on the laptop.

I have Mageia dual-booting with Win7 on a graphics tablet, but I use that most for watching old movies and TV shows and some testing.

Linux has been my primary OS since 2004 when Slackware v10.0 was released. I'm currently running a dual boot of Slack64 v14.1 and (for testing purposes) Win7. My last machine never saw any version of Windows; I bought it in 2005 with Xandros on it, decided that I preferred Slackware, wiped the Xandros, installed Slackware, and used that machine (keeping up with each new version release along the way) until last year. That's when I decided it was time to make the move to x64 and built myself this machine. I call her Lucille. :)

Debian on my desktop, ChromeOS on my laptop. I also have Debian in a chroot on the chromebook, just in case, mostly to run Thunderbird (Iceowl) since there are no real email clients for ChromeOS. CloudMagic is available, but it's still not ready for prime time.

Xubuntu on the desktop machine, Linux Mint MATE Edition on the EeePC netbook.
I do run Win XP in a virtual machine on teh desktop because I am my political party's local treasurer, and the Canadian government software for reporting our finances is Windows only. (I tried it in WINE but it didn't start.)

Desktop
 

Linux mint Cinnamon on my desktop and laptop computers.

Linux or windows
 

Linux is my main system Window I keep to fix other people computers
Ubuntu /mint is most machines
Ubuntu server for 2 servers
Start into Linux when XP was started have window 3.1 and Ubuntu 9 on same disc
all this great to read so many replies
Linux is the light.

Linux or Windows
 

Linux. Specifically Ubuntu Gnome on the desktop, file server & 3 laptops. Windows XP running in a VM to handle Quicken.

I tend to use windows when gaming, or at work but use Linux for everything else. I spend more time therefore on windows, but still consider Linux my default. This question is a bit too simplistic!

Only Linux
 

I have never used Windows, as I switched to Linux, in 1994 I think, as soon as the 1.0.x kernel was available. Before that, it was DOS - horror! I did use a remarkable piece of software on top of DOS, namely Desqview-X. It was a heroic attempt to overcome the severe limitations of DOS. I began with Slackware, but shortly after that moved to Debian, to which I have been faithful ever since. I made brief experiments with Ubuntu - not bad, but I didn't like the non-existence of a superuser - and FreeBSD, which is also fine, but a bit more restrictive than Debian, and a bit more work to maintain.

I only use Linux (Mageia 5) on my desktop and laptop,and Raspbian on my Raspberry Pi tablet.Having started with Mandriva I used that until they went all haywire so I followed the fork to Mageia.
Regards,Peter

I started with Unix over 30 years age but the realities of business have moved me to Windows desktop. That being said, I always have a Linux VM waiting in the wings when I need to get some things done that are just so easy with the familiar native tools of *nix.

for other
 

Slackware 14.1 I need reliablility so I use lilo boot loader to boot Windows 10 Slackware is the first to boot up and is up and running as soon as I get home from work on the same monitor I have Le Capitan and on the side I have a netbook running Dabian Jessy my phone and tablets run Android they are both Nexus 7 KitKat 4 Lollipop

Opensuse 13.2 on desktop, 12.2 on laptop

PCLinuxOS on desktop, Slackware on server.

Slackware64 Linux.
To scan I run the HP software in winXp in VirtualBox on the Slackware64 Linux desktop.