There and lots of small reasons that ebb and flow with Android release but I have one red line I will not cross:

The OS on any portable computer of mine must always allow me to develop personal use software with no subscription or gatekeeping to the development, installation or continued use of that software.

That, so far, rules out all iOS devices. And really iOS and Android are the only players in the game worth using, so I’ve been and android user since installing the first beta on an SD card for my Windows Mobile HTC Blueangel