I actually went for an Android device, largely because the hardware running iOS hasn't stayed up to date. Mostly I'm looking about LTE support. Also I was interested in trying a large screen, and while I like it, the 3.5" on the iPhone is just fine.
Android is a great OS, it allows for a lot more control, and being someone who likes to play around with his devices, I enjoy that ability. I've also had a Windows Phone, and while I liked the hardware(it had a slide out keyboard) the platform hasn't stay up to date(I'm looking at resolution stuff here) Also the inability to use google's search and maps is a big issue for me.
Currently, I'm using a Nokia E6 running Symbian, which I'm loving for the keyboard and battery life, but Android and iOS have the game wrapped up in apps. Even Windows Phone has better apps then Symbian(for my needs at least) But the UI on Symbian is decent now, and the battery life allows for something I just can't get elsewhere.
Over all, I wish Palm was still around, their OS was top notch, and their hardware offered more choice then the iPhone. Android is a great OS, but the hardware is sub-par on devices that have BlackBerry like designs, while Nokia/Palm made great candy bar QWERTY devices.
It's a shame the market is getting rid of all the choice we had a few years ago(when we were switching over from older platforms like Windows Mobile,Symbian and Palm OS to WebOS, Android, Windows Phone and iOS)
Hardware wise, I think Apple and Nokia have the best game in town, but no one seems to be as dedicated to the candy bar QWERTY phone(outside of RIM, so hopefully BB10 raises the bar for their OS)
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Just pulled the trigger on this:
http://www.google.com/nexus/
I think I'll like it better than my Lumia 800.
Very nice device, I'm considering one. Although the device is a little dated now(just barely) More so when you see things like the HTC One X, but after owning the Nexus One, that phone was amazing, and while the hardware game for Android has improved, the Nexus line is still top notch.
I also have trouble jumping onto the Samsung wagon, it's a shame Nokia didn't pick up webOS, while I know that's a deadhorse, I just can't jump into Windows Phone ecosystem(and honestly, I tried)
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which amazingly, has nothing to do with the WP7 platform or Nokia failing.
Sorry, but I think the ability of a platform to ensure it will be around in a few years could matter to some people. It's not a deal breaker to me(I bought webOS hardware and apps for it) But I can see why the position Windows Phone is in today might effect people's eagerness to buy it.
That said, Nokia is a huge name as is MS, so I can't see the platform ending up anywhere better then 3rd place in the mobile OS market.