Well, ill give you my input. I'm a diehard blackberry user dating back to os5, and I've had the z10 and Q10 for a year before switching to WP8. I love Wp8 over 10.2.1 for many reasons. It's fluid and doesn't need resets or reboots, animations of OS are great looking and don't seem cumbersome, and overall the OS is just so fluid and efficient. Yes BB10 was designed to be a very slim is in terms of Ram usage, and don't get me wrong, it's a very efficient OS,fluid and I loved using it but there's just something about WP8 that got me to switch. I wanted to try something new and fresh and I'm staying with WP8. The apps were never a factor because WP has everything I had on BB10 (snapchat, insta, dropbox, ESPN just name a few) also knowing that wp8 runs the same if not quicker and smoother than Bb10 on 1 gig less of ram just amazes me. Battery life is loads better than my z10, but that combines both hardware and software.
And to elaborate a bit on the apps, it was a great addition to be able to load apps from amazon app store, google play store, but they just didn't feel the same running on bb10, you could feel a bit of lag, the android interfaces,etc. So while it satisfied my needs like candy crush, any.do, duolingo, I don't think the android runtime on bb10 is enough to entice users over wp8.
With that said, I would get a Z10 as back up since I would like to switch between different OS, rather than having two windows phones. I did it for a while with my z10 and s3 before I sold both and got my L925
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