parenthetical aside with "to"
This sentence, to me at least, seems fine as is.
In this sentence, I believe "to me at least" to be a parenthetical aside, and it looks completely acceptable. But my English teacher said that I ALWAYS have to move "to me at least" to in front of the sentence like this.
To me at least, this sentence seems fine as is.
I think that is just a type of style, as I have numerous sentences that resemble my first sentence in structure. But because I am not a native speaker, I just have to make sure.
Are both of them fine, or is it just second one that is acceptable?
Congratulations, and I mean that sincerely, you have reached the stage in your understanding of English grammar at which you know more than your teacher. At least in the matter of parentheticals. Where to place a parenthetical is a matter of style. Since parentheticals by definition are asides, interruptions in the main flow of a sentence, they should be set off by the appropriate punctuation, of which you have three choices -- commas, parentheses, and dashes. For your short, four-word aside, commas are appropriate. The determination relies on the length of the digression, the closeness of its sense to the sentence, and its own internal punctuation. Your style guide -- either the one you've chosen or the one thrust upon you -- will have an appropriate discussion. I favor The Chicago Manual of Style, which has numerous examples of parentheticals in mid-sentence.
To expand on your example, suppose you had written
This sentence of death, to me at least, seems fine as is.
Here, as a matter of style, the interruption after the stark nature of the sentence in question, heightens the anticipation of your readers as they look forward to your judgment on a capital case. And that judgment belongs to you as the author, not to some list of rules handed out in English class.
You are right. To me at least is as you say a parenthetical, and (with appropriate disjunctive pointing) it may be placed in any of the marked positions:
^This sentence ^ seems fine ^ as is ^.
I suspect your English teacher is offput by the splitting of subject and verb - s/he would prefer that "the sentence seems" never be torn asunder. Many who were raised on the "no split infinitives" rule were also taught (and/or just sort of extrapolated to the point of believing) that it's bad form to separate ANY subject from its verb. Of course, that has never been a true rule, and even the split-infinitive rule has been out of favour for half a century. ("To boldly go..." dates back to 1966!) So, you are right and your English teacher is wrong. Your sentence, by present-day standards, is absolutely correct.