温泉に行ったらどこがいいでしょうね。hmm not natural. 温泉に行くならば can be replaced. 温泉と言ったら、どこがいいでしょうかね。means quite similar. When it comes to Onsen, where would be good. かな？？
The example of zero is most natural. Otehr suggestions are not as good.温泉に行ったらどこがいいでしょうね is simply unacceptable."When it comes to Onsen, where would you suggest?" would sound natural in English.
Not as good? You shouldn't say so as we use them except 温泉に行ったら even if you use only what you call the most natural one. 心外なご意見です。（・＿・）
Sorry, I did not realize that "other examples" included 温泉に行くならば and 温泉と言ったら. Both of them, of course, are acceptable even though I would vote for 温泉といえば.
##5234 Japanese is not natural. この質問に答えるとしたら、 何をもらうのですか？ この質問に答えたら、 何が貰えますか？
Is this actually how to use a subjunctive mood in Japanese? I wasn't sure if such thing existed. For example, "If I had been born rich, my life would be better." or "If I were President, I would feed the hungry." -- Both meaning "X is not true, but if it were, then I think Y would happen." The emphasis is on the requirement that "X is not true." Does this nuance come through in the Japanese?
金持ちに生まれていたら生活がもっと豊かだったろうに or 大統領であるとしたら、飢えた人々を救済したであろうに - both of these examples satisfy the supposition " that X is not true" but if it were, then Y would have happened.
I think of this as more of an "assuming that..." or "if we assume..." construct. It's basically saying, this might not be correct (or might not happen), but what if it is (or does)?
For example: 本当だとしたら、どうするの？ Assuming it's true, what do we do then?
I updated this to Level 2 because it's in the 2kyuu review books.
~(だ)としたら is commonly used to refer to something that was said before, e.g. in a previous paragraph, or in reply to the person your talking to.