Honestly, truly? To find the best soup in New York, one has to go to the best restaurants. Daniel (60 East 65th Street; 288-0033), for example, serves heavenly, rarefied soups -- but one can hardly belly up to the bar during lunch hour and order one ("avec les oysterettes, garçon!"). So we asked Larry Thomas, the actor who played the Soup Nazi on Seinfeld, whether he had a favorite city souperie, but sadly, he's only been here four times in the past fifteen years, "and each time, I have pizza." Well, Mr. Thomas -- no soup for you! Barbara Kafka, author of Soup: A Way of Life, recommends a $5 bowl of pho, the beef-and-rice-noodle staple of Vietnam, from Nha Trang (87 Baxter Street; 233-5948), on the Lower East Side. For busy midtowners, we're hot for Tuscan Square (16 West 51st Street; 977-7777). This sprawling gourmet market usually serves four soups each day from a repertoire of about 30; all come with freshly sliced bread. Chef Patrick Nuti uses a medley of unusual vegetables for his creations (the ribollita contains black and white cabbage, for instance), and all of them are so thick, your spoon will stand up and salute. The soups are vegetarian, nondairy, and (on weekdays) self-serve -- thus guaranteeing each customer control over the ratio of broth to good stuff. "I am young," says the 29-year-old chef, "but at this, I know I am a master."