Quick reply...
Android? Big no. I never enjoyed Java, and Android does sound too restricted. Replicant may be more open, but still, Java is not something familiar. Do they have GNU Chess on Android? GNU Octave?
Jolla... Was curious. Heard their hardware is bit cheap. Playing on UI, colours and other halves, not the device itself.
Lumia? Big no. At least, as long as it has Microsoft Operating System Only. If it had hw qwerty keyboard, Pureview camera and was capable of running Nemo-Mer or Fremantle-Maemo, that would have been a different situation. And a different device, too.
Neo900... Crazy? Maybe. Hardware? Excellent. Operating system? FOSS-fremantle, maybe Nemo-Mer, SHR, Replicant, Debian, whatever... For the sake of continuity and legacy, I will likely choose FOSS-fremantle.
Firefox OS? So far, I have only seen a 'cheap' device running it. Maybe, there are high-end devices running it, too. Do they have a hw keyboard? Good camera? Is it possible to get GNU Chess, GNU Octave, espeak, pocketsphinx running under Firefox OS?
HTML is pleasant. But I doubt that porting all applications of the world to it would be an easy task.
iOS... Absolutely no. Shiny candy. Like pepper mint - not my choice.
BlackBerry... Touch-scroller is good. Better than four arrow-buttons and one OK button. Less moving parts means longer durability. HW is not that bad; maybe, I can get used to form-factor without slider and with permanently accessible hw qwerty keyboard. Do not forget to include good camera, and such (good audio, for example, is paramount, both for phone-calling and for music-recording). But, Operating System has to be either Fremantle-Maemo or Nemo-Mer. Possible? No?

Neo900 is an European tech company, too :-)
Best wishes.
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Per aspera ad astra...