Android on a Droid Razr Max HD. From what I can tell it offers a mostly unadulterated version of Android OS. I know its not 100% unadulterated, but compared to other smart phones I have seen it seems less butchered, and I like that.
I wouldn't touch and iOS device just because of Apples draconian attitude towards ownership of their products. To me it says you are not buying an iOS device, but the "privilege to use it only as Apple sees fit". I want to be able to use my phone how I want to use my phone and screw you apple.
Apple does have a nice eco-system doing for itself with the tablets, desktops, laptops and phones supposed to interlink (although I don't know how well they do this, since I have never owned one).
And I just can't get into Windows on a phone. Played with an old one of my brothers for a couple days and just got annoyed.
I like the idea of Ubuntu coming to a phone, as its currently my favorite OS, but not sure when that will happen, and happen on a good device.
For now I'm sticking with Android and the Google eco-system as I look for my first tablet and contemplate rooting my phone and loading an alternate android OS on it, since the warranty period is about to expire.