Weird question: Surface, Lumia 920, or Kindle Paperwhite?
I think for right now the Kindle is the safest bet, and is a joy if you love reading. My advice would be to buy the Kindle, and then save for a Surface (or a Lumia 920 if it gets great reviews).
Amazon does a really good job updating their older hardware. If you don't break it or lose it, the Paperwhite will last for a long time. It's the best value of the three.
I had the same problem just before Amazon announced the paperwhite. Like I said I have a Lumia 800 and was thinking about getting a tablet, my first reaction was the Google Nexus or the Kindle Fire (both are really cheap for what you get). I was going to use it mostly for reading, so when Amazon announced the Kindle Paperwhite my mind was made up. I’ll get the E-reader, it’s small and it lasts for weeks. Bottom line is, I don’t need a new phone (the one I have does the job), I don’t need a tablet, but I read a lot.
1. The next part depends on how much you love to read. If you love it more than enough and have got a computer of some sort (laptop or desktop) you will be served best by the Kindle. It's an absolutely fantastic reading device, and this route will cover all bases.
2. However if you do not have a computer at all, buy Surface Pro. It is a full fledged computer which is quite portable and will serve decently as a ebook reader while doing computing work brilliantly.
3. If you have a computer but are need something really portable for on the go works, get Surface RT. Portable and will still gets the job done and will be better as a e reader than the Pro for a slightly less weight.