The Niagara, Catawba, and Concord yield the most fruity, distinctly mild flavors of any grapes that I know with the exception of the German "Bacchus" grape. (It is definitely one of my favorites, but it is extremely difficult and expensive to find in wine shops in America.)
IMHO, the best American wines using American grapes are by Meier's and by Firelands.
Anyone who hasn't tried them really should. They are the return of the Great Lakes wine industry that was killed by Prohibition.
It is obviously a matter of taste and preference, and to each his or her own. For table grapes, many prefer American grapes.
For wine, it is a different story. Some hybrids are OK, some are good, but none really shine the way some European grapes do. There is no hybrid that can rival a cabernet or chardonnay for popularity among the world's wine drinkers. It may find a niche market among those familiar with it, but they cannot stand up to head to head competition for the vast majority of people.