I have grown a few sweet varieties over the years but my favorite and current type is the Prime-ark freedom.
they are very large, very sweet and very productive. Being primo-cane, they put out a massive cop over about a month in mid spring. ( on new growth). Then a heavier but slightly smaller berries in late summer to frost. I planted 6 bushes. This year I got about a gallon of berries every other day for several weeks. They have now started flowering on the lateral branches for my later crop. They are erect plants very tall and thornless.
I have had brix readings of 15 on these blackberries. They make great wine, syrup and jelly . I highly recommend them