What's the difference between 言わないでほしい and 言ってほしくない ?
If the intended message is "I don't want you to say it" which of the two above would be more suitable?
You can use these sentences in two ways. One is to use it as in "I don't want you to say x (literary)". Another is to use it as in "I resent what you already said".
So, what's the difference? In the first case, 言わないでほしい is an explicit request. 言ってほしくない merely states that you don't want the other guy to tell anybody, and the request is only implied. As a consequence, the latter is softer, as it would be in English.
In the second case, 言わないでほしい focuses on the fact that you don't like to hear x. Hence it is possible to use this expression when you think the speaker is saying something legitimate, but you just don't want to be told that for personal reason etc.
For example, you may say わかってるから言わないで when you are told something that you know you can't defend, but nevertheless want the other person to stop saying it. Here is an example of this usage. The author doesn't disapprove the motivation itself, but he is explaining that one should not say 頑張って. Note however that you can use 言わないでほしい to express disapproval/disagreement. It's just that you can also use it when you don't want to.
言ってほしくない is much less suitable in this situation because it implies that you believe the speaker is saying something unjustifiable in your opinion. For example, if you'd say わかってるから言ってほしくない, the listener will sense a frustration or disagreement, and that he/she doesn't really mean わかってる. More natural use of 言ってほしくない can be seen here. The author uses 言ってほしくない because he pretty much disapproves the word ヤバイ itself.
This is a question of whether the predicate presupposes the excluded middle. In principle, there should be three possibilities:
When the three possibilities exist, the sentence negation of 1 should mean either 2 or 3. When there is a presupposition that 3 is excluded from the possibilities, then the negation of 1 would mean 2, which is the negation of the proposition. In that case, negating 1 is usually preferred over using 2. WIth English
means the same as
and the former is considered the correct form. With English
I can think of one situation where you use 言わないでほしい instead of 言ってほしくない, when you use the phrase as a request:
The first sentence above is a common way to say "please don't" and is parallel to 「言わないでください」 while if the second sentence is used as a request it would sound indirect like "I don't want this told to anyone." It sounds like a statement but you can imagine what's being implied if it is said straight on your face.