I like Android for a couple of reasons. The first is that it slots into the Google Apps ecosystem that I built much of my online life around prior to getting an Android phone — an excellent Gmail app for starters, but also my use of calendaring has improved significantly since getting my ADP1.
The second is that it’s Open Source. This means that (provided you have a suitable handset), it’s possible to obtain or write your own custom firmware which lets the phone do more than what its manufacturer intended. This, for me at least means running later versions of Android well past the support of the manufacturer.