Not a phone, but I really liked the Blackberry Playbook's QNX system. It was extremely smooth and easy to use, and was fairly easy to develop for.

They shit the bed by betting on Flash, which was a dying tech, but I was pretty sad when Blackberry just went to "another Android phone", since I thought what they had was pretty neat.

Blackberry definitely had much better marketing than Ubuntu has ever had, and for reasons probably too complicated for me to fully understand, they're sort of a joke now.