"I have never said" versus "I never said"

I have never said this.
I never said this.

• Is the usage of have in the first sentence justified or grammatically correct?
• What is the difference in meaning?
• When should I use one form over the other?

"I have never said this" is in the present perfect tense and implies that at no time in the past have you ever made the utterance that "this" refers to. You might say this in response to an accusation that's shocking to some degree: "You told some of my friends that you hated me!", "No, you're wrong, I have never said that".

"I never said this" is in the simple past and implies that in one particular instance that is understood by the context you did not say what you're being accused of saying. "Did you tell Dale that you were going to wait for me on Tuesday?", "No, I never said that".

Note that in both constructions, it's probably more usual to use the demonstrative adjective "that" rather than "this" -- why? Because it seems to me that these phrases would most likely get used in response to a particular point by someone else said previously, and so you want to refer to that particular point.

If someone had a written phrase on paper, pushed it across the table to you, and then said "we believe that you made this statement", then you might look at it and say "No, I never said this" where "this" indicates "what's written on this paper".