The word “best” is an adjective, and adjectives do not take articles by themselves. Because the noun car is modified by the superlative adjective best, and because this makes the noun car definite in this context, we use the. Assuming that the passage in the question is about the thinking of someone who is faced with choosing a course of action to take, not evaluating the outcome of an action already taken, I would use best as an adjective. This implies that Mr. Smith is no longer the speaker’s teacher.<\/p>\n