1. Open-sourceEveryone has a different taste over the layout of their smartphone aswell as the graphics. Android is open-source which means you are allowed to do whatever you want with it. You are free to modify the system apps to your needs such as adding a few extra options in your Settings, re-arranging some stuff, adding more cool features aswell as theming it however you want.
One of the biggest websites for Android hacking is http://xda-developers.com - In there you will find lots of developers sharing their wonderful work with the users.
2. Support by many manufacturersAll of the top manufacturers today use Android as their primary OS on their smartphones. Unlike Apple, all of these manufacturers build their devices with a different design, different specs and all for different prices.
Samsung, LG, HTC, Sony and Motorola for example all use Android OS on each of their devices that come to the market nowadays.
You have a choice of all kind of different devices. If you are not happy with the design and specs of one device, you can choose another one.
There are also many good Chinese phones to choose from if you are broke.
3. Variety of screen sizesWhy should you be stuck with one screen size for years waiting until a new device comes out? Just like TVs and computer monitors, you should have a choice of what kind of screen size fits your needs.
Android devices come with a huge variety of screen sizes and pixel density. There are devices offered cheaply with decent displays, and there are devices offered for an expensive price but with HD quality again, variating in different screen sizes. You just have too much choice here.
4. Free AppsThe Google Play store has thousands if not, over a million reached by now. Widgets, weather apps, communication apps, games, and many more cool apps. It is said that Android platform offers you way more apps for free than Apple's iOS.
5. Connected with GoogleFor those of you who don't know, Android is owned by Google Inc. and that means that absolutely everything you use on your Android smartphone is connected to Google. You have Gmail, Gtalk, Google Maps, Google+ you can sync your e-mails.
Absolutely all of your data stored at Google can be backed up with your device and you can access it at any time you want.
Android OS to this day still keeps on growing and is being distributed on a lot of devices.