When the initial Amazon Kindle was released in 2007 you genuinely didn't need to consider why you were getting it - you wanted to get an e-reader and it was a class ahead of everything else out there.
Since then, however, Amazon have developed a number of different versions of the Kindle ranging from the pretty basic e-reader to the high end tablet, all of which are great for different reasons.
Here are the key things to review when buying an Amazon Kindle to ensure you get the right version for you:
1. Why will you use it? If you simply intend on using your Kindle to read e-books, it doesn't need to be one like the Kindle Fire with some of the more up to date functionality, such as web browsing. Really, it probably doesn't need a keyboard. However, if you think you'll be browsing the internet, making the most of all the apps you can get, playing a lot of music, etc, you more than likely want to purchase an actual tablet such as the Fire rather than keeping one of the earlier models.
2. Do you actually need a tablet rather than an e-reader? If you're already used to using a Kindle and want to stick with the format but want extra functionality, get hold of a Kindle Fire, either the standard version or the High Def one if your budget allows. The Fire is quite a compact tablet, compared with others on the market, and will let you to do pretty much everything any other tablet allows you do.
3. Where will you use your Kindle? If you plan to use your Kindle when you're out and about you'll likely want to invest in one with 3G capability - like the Kindle Keyboard 3G or the Kindle Fire. Again, consider what you'll actually be using your Kindle for, if it's simply reading e-books on the train to the office or on the sun lounger on vacation, you may not need internet connectivity (just download the e-books before you go!). Know that the standard Kindle does not have 3G functionality.
4. What special features do you want? The various members of the Kindle family come with different feature to suit their function. For example, if you think you'll use your Kindle primarily for reading e-books you might want to go for the Kindle Paperwhite which has improved screen resolution than earlier versions and a built in light to improve the illumination of your screen. If you believe you'll want to make notes when reading, get yourself the Kindle Keyboard. If you want to do more than an e-reader will let you, get hold of the Kindle Fire tablet as a preferred choice.
5. Are you bothered by "special offers? Specifically for the Kindle Fire (both standard and HD models), you can get a less expensive model if you are okay with receiving ads - also known as "special offers" - presented on the Kindle's lock screen. If you feel you can handle this, you can get some discount irrelevant of the model of Kindle you buy.
One other thing to consider is that Kindles normally only come with a USB charger as opposed to a mains charger (however this is not always the case), so do check the specs to see if you need to get an actual mains charger, otherwise you'll have to rely on the more time consuming USB charger that does get supplied with each Kindle.