～は止めた方がいい　or ～を止めた方がいい


I really don't get why I usually see that people use は instead of を in this
case. The reason why I do not understand it is this sentence:

> ～を選んだ方がいい

I have seen people using this sentence without は. Then, my question is: Why ,
in this specific case, with the verb 選ぶ people use を but with 止める people use
は?




は replaces を (or が, or follows after other particles) when the information
_after_ the は is _more important_ (or "new to the listener") than the
information before it. That is clearly the case with 〜止めた方がいい - the speaker
and the listener are both familiar with whatever is being referred to before
that point; it's the "you'd better quit that!" part that is the main purpose
of the sentence, so は is used to emphasize that latter part of the sentence.

Meanwhile, 〜を選んだ方がいい is more neutral in terms of "which side of the sentence
is important", and using は would imply that the thing being chosen is already
understood as the topic of conversation - it's the fact of choosing it that is
new - and that's just not a common scenario.

I frequently like to consider, when choosing whether or not "to は", what kind
of question the sentence could be in answer to, as that dictates whether or
not は is appropriate. If it could answer a question where a question word
occurs in the part of the sentence before the particle, then you don't use は,
otherwise you probably should.

> これは何ですか？ → これはペンです
>
> だれがいますか？ → 山田さんがいます
>
> これは、どうしよう？ → それは[止]{や}めた方がいいよ
>
> どの道を選んだ方がいい？ → 右の道を選んだ方がいい

