I'd love to go all in on Apple but I can't justify $1000 or so on a phone, even the 5C is about $900.
I use a Windows PC and and prefer Outlook.com/Sky Drive to gmail/Google Drive so for me that's about that. I can see value in Chrome Books but for me I'd rather spend a more on a machine that will do everything I want rather than one which is likely to have limitations.
As far as apps go there simply aren't that many I need and Windows Phone covers what I do need. I really like the way contacts are managed on Windows Phone and for me a phone is primarily a communications device.
The Android flagship phones, about $1000 on launch, are great for that money I'd want better integration into other devices such as with Apple. Below those it really is patchy. Updates might take a long time coming or not be compatible or the experience might just be awful because of bloatware from the device maker.
At the $500 or below mark the key word is 'consistency'. Does it do what it says it will first time, every time? For that the Nokia's are hard to beat. Some Androids would be better but why take the risk?