I've decided to talk about my favourite mobile platform at the moment: Android
I don't like the iOS platform because of a few factors; for example, as with most of Apple's other products, you can't just buy a product, you have to buy something else to make it work, in this case, iOS is designed to run on iPhone only, just like how their MAC OSX operating system is designed to only run on MAC computers. Apple are also too restrictive on their app store, which is why they're having problems with jailbreakers. What I love so much about Android is that there are barely any restrictions; you can send files over BlueTooth without having to hack your phone's software, you can do whatever you want with your phone. If you root your phone, they even allow apps that will only work on rooted phones to be distributed via the market!
It's open source, and has a very active development community.
Aside from this, it's very user-friendly as it is integrated with the Google products and services that we've come to know and enjoy, it has a very familiar interface and is packed with tons of pre-installed apps that prove to be very useful. You will find that most mobile phone manufacturers have at least one android-enabled phone on the market, even the small phone manufacturers.
The main thing that I don't like about Android is it's development platform. I cannot stand Java, it is a horrible language in my eyes and doesn't really make much sense to use. It seems like a waste of resources. They should at least make a decent native API available for developers.
If you haven't already, you should check out a phone that has Android enabled as it really is a nice platform.