Mmm. While not a classic Nova, the MiniNova is still going and about a year older than the BS2. Hard to guess which one sold more. I think the MiniNova has wider appeal, polyphony, effects, voice, like the eternal microKORG, but the BS2 has seen more updates to keep it on people's mind.

That said, of the two the BS2 is the one that I see has more likely to be replaced by a new model, to keep up with its own updates, people's wishes, and the times.