"Which one is the best" is obviously a question format, so it makes sense that " which one the best is " should be the correct form. This is very good instinct, and you could even argue that the grammar is good, but at best it's unnatural.
Which is correct: "one or more is" or "one or more are"?
Which came first when saying numbers: "one hundred AND one" or "one ...
The first example is incorrect. The second and third examples are both correct. Which one you use is mostly a matter of preference, although a hundred appears more frequently than one hundred. There is also another form, an hundred, which was common in the past, but has mostly fallen out of use. See Google Ngram Viewer: a hundred, an hundred, one hundred:
You typically wouldn't use either phrase for meetings. 'One-to-one' is rare and often technical in any case, you might say, 'On most websites there is a one-to-one relationship between a username and an account,' meaning that there is only one username per account, and only one account per username. As @FumbleFingers said, 'one-on-one' tends to suggest physical activity, or at least ...
As @PeterShor points out, in this case "one" is the pronoun, and would never be numeric. Beyond that, as a general rule, spell out numbers 1-9, but for technical writing, it may be appropriate to always use the numeric version when you're referring to a numeral (as opposed to the pronoun example above).