I prefer
This is the best performance I have ever seen.
over
This is the best performance I ever saw.
They mean the same thing (namely, that the person saying it witnessed the best performance thus far in their life) unless context implies otherwise.
This is the best performance I will ever see.
The sentence means they will never see a better performance; it's impossible for another performance taking place in the future to be better than this one.
1) It has been a long time since I visited you (at the hotel).
I visited you at some (distant) point in the past.
2) It has been a long time since I used to visit you (at the hotel).
In the past I visted you on a regular basis, maybe once a week. At some (distant) point in the past, I broke with that habit.
3) It has been a long time since I have visited you (at the hotel).
I visisted you at some (distant) point in the past. I probably have visted you more than once, but that doesn't mean it was a habit.
So, yes, 2) and 3) could have a similar meaning, but 2) really draws attention to the fact that the visiting was happening on a regular, habitual basis, and it is the habit that stopped a long time ago.
Just for illustration, let's look at a different example.
Suppose I used to live in city A, but I have now moved to another place. While I lived in city A, I visted a certain restaurant once. Also, I was a regular at a bar (I was there almost every day). There was a cinema too. I went there a couple of times, but I'm no great fan of the cinema.
Now, after some years, I could say:
It's been a long time since I visted that restaurant. It was a really great experience though, maybe I should go back there some day.
It's been a long time since I used to frequent that bar. Nowadays I just drink alone, at home...
It's been a long time since I have been to that cinema. I don't know if that nice girl still works there.
Best Answer
You can say either was or is. (And I will also explain what it means when you say had eaten.)
Using was sounds natural here, and it belongs to your description of your visit to the restaurant, which occurred in the past. In other words, using was fits the narrative perfectly, especially in terms of flow: it uses the same simple past tense that all the rest of the verbs in the narrative use. Unless you tell us otherwise, we assume that it is still the best food you have ever eaten.
If you say is, as in
This is also fine. You need to note that the present tense is does not match the tense of the rest of the story (of your past visit to the restaurant). So it does not flow as naturally However, if you want to stress that the food you ate at that particular visit is still the best food you've eaten when you say your sentence, then you use is.
As for using had, as in
This is also fine. But now you imply that it was the best food you had eaten at the time you ate that food, but that you have eaten food since then that has tasted better. It was the best food you had eaten at the time you ate it on your past trip to that restuarant; however, it is now no longer the best food you have eaten, because you have eaten food since that trip that was better.
As for using the verb to have instead of to eat, as in
This is okay in spoken English. But it is informal. See definition 4 (Oxford dictionary), so it is okay for the simple present tene and simple past tense.
However, many English speakers might avoid saying
because it sounds bad due to the double use of had and the alternative eaten is available.
I disagree with the answer by CookieMonster when it says
"If you're talking about the action of trying that dish for the first time as part of the list of things that happened with you during your stay there, then use was and shift the present perfect tense down to the past perfect one on the time line:
As a native speaker I can say that this is not true. I don't know why CookieMonster says this. Perhaps he/she doesn't have a good grasp on sequence of verbs. There is no reason to "shift the present perfect tense down to the past perfect" when you are narrating a past trip.