Azure tables is good for storing data much in the same way as a spreadsheet, however when you want to do anything even slightly complicated to index the data it soon becomes hard with table storage and you have to start repeating data. Not ideal. Cloudant makes it very easy to store the data and index it in a myriad of ways without repeating any data.
-Recommendation by the Windows Azure team.
-Scalability.
-After I got my head around CouchDB in a weekend it was so easy I didn't need to look any further.
I've only just started developing for Android (Foundbite's next version) so can't really give an opinion. Visual Studio is great to work with though. There are only 4 screen resolutions for Windows Phone so in that sense it's easier to develop the UI.