Personally, I would activate my Z10 and use that. I think BB10 is the most intuitive OS available, and the granular control is amazing. If you are leaving because of the App shortage, I would probably pick up the One+ One or the HTC One. I have been on android before and thought it was okay. My only complaint was the terrible wait and/or lack of updates to the OS. I'll reserve judgement on iOS8 until the devices are available. $700+ for a phone is a large commitment, so I tend to lean away from Apple Devices. Thankfully, I am happy with my Icon so I don't anticipate updating my device for some time (unless they release a variant with an SD card slot. <3
~Ex