To express the idea "that movie was so good that I’m absolutely sure that I will not see a better one in the future," one could say:
"This was the best movie I ever will see," or
"This was the best movie I am ever going to see."
This is such a strong opinion that it would usually be stated with some context before it; for example,
"This was not only the best movie I've ever seen, I think it is the best movie I ever will see."
Finally, in English, in real life, we do not really rely solely on the verb tense to express our meanings. The verb tense is one of many cues, and not a very strong one. If you are <em>writing</em>, it is up to you to make your meaning clear. If it is important to express what happened first, and what was happening when something else was happening, usually you should need to do more than use the right verb tense. If you are listening, other words in the sentence will tell you what the speaker means.
For example, if someone says "Yesterday, I am walking down Sycamore Street and these little kids are drawing the rainbows on the sidewalk in chalk," we know that he means "Yesterday I <em>was</em> walking" and "These kids <em>were</em> drawing."