The best tasting early grapes I have are King of the North and Edelweiss. I think KOTN is very underrated. It hits 20 brix for me and has thinner skins than Concord, but the berries are very small. Edelweiss is also early and very fruity, but I think it blooms earlier than other labrusca type grapes and is therefore more susceptible to frost at bloom time. Early Campbell is also good, but might only be a week or two earlier than Concord. Buffalo is decent. It tastes sweeter than Concord but has less of Concord’s “grapey” flavor. I don’t think it has higher brix, just less acid. I like Concord better, but Buffalo is much earlier. I think KOTN, Edelweiss and Buffalo are a solid month earlier than Concord. Side Note—> All of this is based on only three years of experience with these varieties.
Here’s a link to a previous reply of mine that gives a few ripening dates: Table grape ripening order / are Concords worth growing? - #4 by ztom