Erm, that's hard. I would prefer Android's UI over windows but because of my own reasons I'd rather not get too entrenched in Google's eco-system (having to do with all their stuff integrated and if you are on G+ for example and if you break a "rule" they block access to *all* your google services. I don't want to be too much at the whim of Google cause of that since I do enjoy G+. Oddly enough while I like G+ it's what has made me a bit paranoid of Google. Though I at least trust them a lot farther than FB).
And I hate the Windows phone honestly, blech.
I have a feeling I'd cave and go with an Android, probably a Nexus device to make sure I can get the updates when they came out (updates are nice, they make you feel like you got a new phone in a way). And hopefully I could find a good high end Android phone that isn't ridiculously big (honestly, I prefer smaller to bigger but it seems the iphone is really the only high end phone that hasn't fallen to the bigger is better fad, well now it has but only a little bit at least).