No way you could just name one New Balance that is a must-have for the sneaker rotation, although the classic "steel grey" 1300 is a good a place as any to start. The brand takes style and comfort to another level and, their "Made in USA" line should be a necessity to the American wardrobe — and any collector's racks. If the 1300 isn't your style (who ARE you?), there are always the custom options of the 574 or 993, or other USA-made classics like the 990 or 998.
Alternatives: New Balance 574, New Balance 998