In general those grapes allow you to grow grapes where it is too cold for vinifera grapes. They can make some very nice wine but in general have 2 to 3 times the amount of acid in them over vinifera. Marquette and LaCrescent are easier to work with than Frontendac but they all have their own strong and weak points.
I got this started now let's hear from some others to fill it in for Goldry.
Marquette - I think my favorite hybrid grape for flavor and the wine. It has been spotty for us in zones 3/4. They are prone to early bud break and frost damage and they seem to have a higher degree of cordon loss than other hybrids.
Frontenac is a solid grower and hardy but the acids are a bit high most years for a dry red wine. It makes a nice sweeter wine. The white varieties (Frontenac Gris and Frontenac Blanc) make nice off dry to sweet white wines. They are just as hardy as the red frontenac.
I love the flavors of La Crescent but we just can't grow it in ND. Yields are very low.
There is a new white grape from UM called Itasca. I haven't worked with it yet but I hear promising things about it. I'm looking forward to see how it does in our area. Several growers are going to be putting some in the ground this year.
The better flavored red grapes I think are coming from private breeder Tom Plocher. His petite pearl has been out for a while now. It is a little slow growing and does have trouble for us, but closer to zone 5 it seems to do well. His new red variety, Crimson Pearl, is awesome and seems to be hardier than PP. He also has a new variety called Verona.
The breeding program at NDSU has some promising leads for cold hardy grapes. I know several promising whites and reds are moving forward in their trials. They seem to survive and produce balanced wines. That might be several years off yet.
I'm growing Marquette and Petite Pearl. They both make decent wine, but the jury is still out as to how good. Right now with early tasting on 2016, I'd say I prefer Petite Pearl.
The biggest issue with Marquette is early bud break. If I had understood this when I planted, I might have only planted Petite Pearl. It's a real issue and one of these years a late frost is going to zap my whole crop. Petite Pearl breaks out about 10 days later than Marquette, even with double delayed pruning on the Marquette.
The Marquette also gets so high in sugar, therefore high in alcohol. I harvested last year at 28 brix. I watered back to 25.5 at fermentation, but I'll take it back even further this year, like 24. There is a presence of alcohol in the Marquette. I don't know if there is any way to fix that before I bottle.
I live in zone 5a, we hit -25F this winter, and everything looks alive. I don't have any issues with ripening as I get about 2700 GDD each year. This year I am experimenting with some Pinot Noir and Pinot Precose, which will require heavy winter protection, if they will survive at all.
Just pruned my Frontenac and Frontenac Gris vines. Now is the time. Last snowfall (6") just melted early this week. Frost is starting to come out of the ground. I hope to get a nice yield this year. And per Grapeman's previous advice will be patient and let them hang until good and ripe. I believe I will also invest in a refractometer. Last years yield is still bulk aging. Hope that helps mellow it out some.