Why not Android? Because...
Android has a lot of ardent supporters out there in Internet Forum Land.
It shows serious potential as a portable operating system and is improving with every iteration. You can make it look and behave pretty much however you want. Development for Android is free. These are all great reasons to support it (and I do support it, I believe that choice is a good thing).
But there's exactly one reason why I'd never choose it for myself.
If I buy from Microsoft then I am Microsoft's customer. Their priority is to do their best for me so that I continue to buy and use their stuff.
(You could almost apply this to Apple but they're pretty much the Scientology of tech; if you buy from Apple you are likely to become a howling cultist with no mind of their own, something I find unappealing).
You don't ever really buy from Google. It's never a case of "I bought this - support it and encourage me to keep spending money on you". If I bought a Chromebook or an Android phone, if I used GoogleTV or Gmail, I would never be Google's customer. I'd be their product.
Google's business model is based on selling information about me to the highest bidder(s).
That kind of freaks me out.
It doesn't really matter how good Android gets (although I hope it gets absolutely superb because that will encourage all its competitors to raise their game). I can't bring myself to be somebody's product. I have a personal, ethical objection to the fact that this company wants to sell me.
In the old days, Microsoft were the devil. They were the Beast of Redmond and evil went with the territory. These days, there are much bigger evils and the way these things work, I'd rather pay for my software and stay free myself than use something "free" and be sold for profit.