It's an unrivaled record. The Maisonette restaurant in Cincinnati has received the Mobil Travel Guide's top five-star rating for the 41st year in a row. No other US restaurant can boast of such a record. Still, business is down at the 55-year-old Maisonette because there are fewer visitors to Cincinnati's downtown as the economy and downtown attractions have slumped. A competing restaurant opened by a former Maisonette chef - Jean Robert de Cavel - has also cut into business. Maisonette owner Nat Comisar is listening to incentive offers designed to lure his contemporary French-cuisine restaurant to north Kentucky. But, no decision has been made. Comisar says he would prefer to keep the restaurant in downtown Cincinnati, if that can be worked out.