I started using Android about two years ago, after using a Blackberry Bold and an Nokia E63. So far, I've had three different devices that run Android and I've really enjoyed using the OS so far.
My current device is a MOBO MB400(Spanish and its a PDF), and so far it's the one I like the most. It has enough RAM, and with an 16GB Micro SD card, has more than enough power for the use I give.
With it, I found that for me a 4" screen is the sweet spot for me. It's big enough for what I use my smartphone for, while fitting my hand as a glove. I used a 5" MB505(Spanish and its a PDF) for about 6 months, and it never stopped feeling somewhat awkward to use for me.
Before coming to use Android, I was somewhat weary about making the jump. Mainly because I really liked the physical keyboard on the Blackberry, and the Android devices with a physical keyboard weren't all that good.
But after talking to some friends about their experience using Android, I decided to make the jump. And since, I haven't looked back and Android is my go to mobile OS.
While the Blackberry Priv was an option for me, since it is an Android device made by a company known for making solid devices with a physical keyboard, I keep coming back to MOBO devices since they give me the best value for the price.
Most importantly, MOBO devices are unlocked. Meaning that I can use them with any mobile carrier I choose to.
At the end of the day, the combination of Android and MOBO is one that fits with what I value most. That is, user freedom to choose the device and mobile carrier that better fits her or his needs.
So, I'm on Android camp for my mobile OS.