Do More Things With The Android
The Kindle, and other e-Book readers, only do one thing, they allow you to read e-books. Yes, some come with Wi-Fi, Internet browsers, etc. but their main purpose is to read books. Android Tablets (and the iPad), on the other hand, allow you to download the Kindle app (or other e-Book apps) and still read e-Books just like normal. But, you can also download other apps and do really cool things like manage your time, play games, sync your Google calendar/contacts/Gmail, etc.
Buy Any Type of E-Book
Once you buy an e-Book reader, you are stuck with that reader's market to buy books. For example, if you buy a Kindle, you can only buy books from Amazon. However, if you buy an Android Tablet (or iPad), download all the different e-Reader apps, you can now access all the e-Book markets and download from any. Some books are only available from Amazon and others from Kobo - with the Android / iPad, that's not a problem.
The Price Isn't That Big A Deal
The price is marginally different. Yes, the Kindle and other e-Book readers range from $100 - $150 and Android tablets and the iPad are in the $500 - $600 range but in the grand scheme of things, $400 difference isn't that much when you think about what you could be using it for and for how long. Spread out over 4 or 5 years, that money difference is less than $10 a month.
Use 3G To Access the Internet On The Go
The Android Samsung Galaxy Tablet can also do 3G internet access just like smartphones. Most cell phone providers will allow you to add it to your existing data plan. Rogers, in Canada, allows this for as little as $15/month. Now you can browse the internet, download books, etc. anywhere.
If you are looking to get an e-Reader, take some time and consider getting an Android Tablet or iPad. While the e-Reader does one thing, read books, Android Tablets and iPad do the exact same thing and more. You won't realize how many you can do or would do with a Tablet until you get one.