You can choose any sweetness level from dessert sweet to bone dry and customize it however you like, so it's totally up to you!
While every juice will taste good sweet (if you like sweet wine), not every juice makes the best dry wine.
Some juices need extra sweetness to bring out their unique flavors. Otherwise, the yeast will gobble away at all their natural sweetness, and the flavor will taste a bit bland and quite acidic afterwards (think lemonade minus the sugar).
These juices should be made at least sweet on the drink designer:
Cranberry (any variety will work)
Pomegranate (especially if you like bold, tannic reds)
Cherry (you’ll have best results with juice that’s only made of cherries — there are many varieties, such as Juicy Juice, that are actually mostly apple juice!)
Concord or Red Grape
Any kind of iced tea