As far as I am concerned, all three can be correct, depending on the context in which they are spoken. None of your sentences is an idiomatic way of saying something. Each one is legitimate in its own way. Here's my summary of how each sentence could be both correct and acceptable:
This is the first time someone says this to me. This sentence would be an appropriate response to the compliment if the person complimenting you is standing next to you and is commenting on something you just wrote, such as the address of a building he or she was looking for. Let's pretend this person is from out of town, and you live where both of you are standing. The "feeling" of the sentence is one of surprise and wonder. You know, "Wow! I've been complimented before on a number of things, but not on my handwriting. This is the first time someone says this to me." It's as if you are inviting the complimenter to join with you in your surprise. Substituting the word that would also be correct and acceptable; in other words, "That is the first time . . .."
This is the first time someone has said this to me. A few minutes after you are given the compliment (in the above scenario), you tell your wife, who was not there when you received the compliment, that what happened (let's say just a few moments ago) has not happened before. In other words, you have searched your past history of having received compliments and have concluded that the compliment on your handwriting is the first time you can refer to the compliment as already have happened.
This is the first time someone is saying this to me. Let's say that a week later you are telling a group of your friends about the guy or gal who complimented you on your handwriting. You are recounting the anecdote in the present tense, which is quite common. For example, you might say in a different situation regarding a different experience that has occurred in the past,
"So, this is the first time a girl smiles at me and then says, 'My name is Mary. What is yours?'"
The above scenarios are not the only way to complete the sentence that begins with "This is the first time, " but perhaps they give you a feeling of how nuanced and flexible the English language can be.
By the way, you could also phrase the sentence in this way:
This was the first time someone said this to me.
In this sentence, the simple past tense is used. The sentence sounds quite similar to your sentence number 2.