Should I get the small or large size of a pour over brew device when I'm only brewing one cup? (eg. Hario V60, Woodneck)
I've had this discussion on more than one occasion with my mother.

All else being equal, our experience has been to get a coffee maker optimal to the size of pots you will be brewing.

By getting a maker too large, the grounds will not receive the hot water in the rate or pattern that is intended for that size.  Having a basket of grounds filled only part-way will not process the water and be able to activate the grounds in the same way as if it were full.

Your best bet is to get a one-serving brewer, especially if that is all you ever intend to make.  If you ever had the opportunity to make more than one, repeating the process would not be as bothersome, since you indicated you would be making one pot at a time for the most part.