I grew up with DOS and Windows 3.11 which lead to Win95, 98SE, XP, & now 7. I've also used Ubuntu a few times and it's my 2nd choice , I've also used Mac 3, 5, 6, 8, 9 & some of 10 and so far haven't cared for any of those versions.

My cousins grew up using Mac & it's what they still use today, I also have a friend who's dad was a big Unix fan and they now use Linux. I believe that the most likely OS a person uses is what they grew up with (I'm talking about those who're 30 or less in which they grew up with a rudimentary OS) and since they become sooo familiar with it, that's usually the track they stay on.

Though these smart phones are a beast all of their own in which case it doesnt matter if it's an iPhone or a Droid or whatever, all those smart phones look, feel and work the same. There's very few apps for one smart phone that isn't available for another.