Houston has the best Vietnamese restaurants in the country -- the problem is picking one. We like Nga's, a little unassuming joint with a friendly atmosphere and a hip clientele. There are all kinds of discoveries on this menu, but the waiter tells us the most popular thing to order is No. 123, do-it-yourself spring rolls. He brings you a mixed grill of skewers and meats on a bed of vermicelli. On another plate are lettuce and basil leaves and a pile of round rice papers. Don't worry if you can't figure out how to roll them up; the waiter will come over and give you a demonstration. The food here ranges from pretty good to spectacular. While the lunch special is always tempting because it's such a bargain, try the hacked duck with mint and dipping sauce sometime. Looking for a real change of pace? Try the parfait of shaved ice and sweet beans in syrup with grass jelly for dessert.