In that scenario, they would always go for option A unless there was some really specific fight mechanic that just happened to be perfect for B. At least in high level play.

As for options 1 & 2. Well that would go to the Secret World example mentioned before. "White shift for this one boss that has higher healing requirements, black shift for everything else" or similar.

Divorcing specs from affecting damage would help. But I'm still pretty skeptical of it overall.