OEM specific OS then
Android all the way.
Newbies try and do it all the time. They see shell and decide its all too complicated.Lol, don't think it takes convincing to avoid running windows on a server, you'd have to be insane! People get scared of the command line based interface, but it's very easy to get used to. Unless of course what you're dominantly serving is a windows only based program
I don't really see what the appeal for the iPhones are. Sure, they're great phones, but so stupidly overpriced! You're locked to all Apple's stupid software, which usually ends up costing even more money, all Apple's certified accessories etc.
Not to mention the integration of Android. If you use Chrome as your main OS on all your devices, they can ALL be synced so you have the same tabs, bookmarks etc available on all devices. To me that is friggin awesome, and also mega handy. You also don't need any stupid certified hardware, I could rig up a nice dock with all the features you could ever need, speakers, video output etc just by looking at the micro USB pin assignments. No special conversion or ID chips.
Of course to the average joe, being able to do all the hardware integration means nothing to them, but if they wanna blow $400 more on a phone because it has Apple written on it, their choice, in terms of actual phone hardware, the iPhones are way behind.