" AOSP is the proprietary part"
No, AOSP is the free and open part. Android Open Source Project - https://source.android.com/
The Google cloud services are the proprietary part (Gmail, Hangouts, G+, etc). AOSP is a fine mobile operating system without any cloud services. Many third party ROMs for Android devices are pure AOSP. You can also put different cloud services in place of the Google services and distribute that to your hearts content, i.e. the Amazon Kindle.
I agree that Windows Phone is a very nice operating system. I tried an htc 8x for a few months and found it very capable in the basics. Email, phone calls, MMS were really quite good. For some people it may be a better choice than Android, though Android improves so fast that it's hard to be confident there. WP is absolutely not "crap" and honestly if we are comparing only the OS itself it is in league with any other modern mobile OS.
There are two serious problems with WP, IMHO. First we all know that the selection of apps is just awful. This is a chicken and egg problem, something Microsoft has had more success than most in solving before, so perhaps that can be corrected. However, the more serious problem is Microsoft's current strategy to create some sort of universal environment (I think a universal environment could actually work, but so far they are just doing it wrong) For example, you mentioned Win 9 providing unified apps that run on a desktop and a phone. This sounds like a perfect recipe for apps that *suck massively* on both the phone and the desktop. I can't see that helping either platform. Same with the desktop vs Metro issues in Win 8... I like Metro on my surface pro but it's worse than useless on my traditional desktop. There may be a way to have one OS to rule them all, but I'm not sure MS is going to figure it out.