That is such a big topic these days!
You mention 2 choices: Windows or Android. Actually, the number 1 choice is Apple iPad - so that makes 3 possibilities. I love my iPad mini, couldn't live without my Droid Razr smartphone, but still need a Windows (or Mac) laptop to get my work done. My husband, Jim, has a Microsoft Surface Pro (true Windows 8 computer in tablet form) and no longer needs a laptop.
If you're primarily 'consuming' content - reading emails, browsing web, using Facebook - a tablet is great, and it can do a little bit of document creation using cloud-based software like Google Drive Documents/Spreadsheets, or Skydrive Word and Excel.
The roadblock in my book comes with pictures. One of my main uses of my laptop is to manage a library of thousands of digital photos. A tablet cannot store thousands of pictures, and it can't access an external hard drive for them either. My favorite software, Picasa is not available for any tablet. Therefore, I still need a real computer.
I've written a couple of articles on this subject. If you'd like to read more, here they are:
What Tablet to Buy?
http://geeksontour.tv/2012/11/tablet-computers-which-one-to-buy/
Can an iPad replace your Computer?
http://geeksontour.tv/2013/08/ipad-as-work-computer/