my vote goes for ableton live, deffinitely. been working with cubase since cubase vst5 version, but when i moved to ableton, i never looked back. Even there is few nice fetaures missing in Ableton, i dont care. Looking forward to next versions as Live 8 seems to getting closer to what i think the best DAW should be.
If you talking about rendering quality, I think it is same, but what I 've spotted, the summing algorhithm seems to be bit different in cubase and Ableton Live..