What smartphone OS do you use?

While it looks like Android is running away with the smartphone market, the competition is still alive and well.
Large herd of Android icons
People have a tendency to identify with their mobile operating systems. They may be saddled with nicknames like fandroids, Apple fanboys, or Windows Phoners (OK, I made that last one up). It's a choice that can feel like an emotional decision as much as a practical one.
The numbers certainly tell a story. Android has hit 81 percent market share for smartphone shipments globally, according to consulting group IDC.
Android wasn't the only mobile OS gaining ground. Dark-horse candidate Windows Phone jumped 156 percent in year-over-year shipments.
Apple's iOS push does seem to be waning a touch in the face of inexpensive Android models, but the company doesn't seem too concerned about it. BlackBerry, on the other hand, seems destined for mobile-OS footnote status.
I strive to be operating-system agnostic. I use a Windows desktop, an Apple laptop, an iPad tablet, and an Android phone. I like it that way. My old Droid X is a trooper, delivering everything I want in a smartphone (except the latest version of Android). When I eventually upgrade, I expect to get another Android phone.
I've shared my mobile OS choice, now it's your turn. What smartphone OS do you use? Vote in our poll and tell us why in the comments.