BB10 is nice. Meego, as seen in the Nokia N9 was a really good UI too. Extremely elegant card interface, that meshed so well with a curved OLED screen. In 2011.

I would love to see an alternative to the iOS / Android duopoly. One way to go would be a better F-Droid ecosystem, and pure AOSP.

But perhaps, even better, a true Linux userland. Maemo lives on with Jolla. Although I hate they still have many closed components.