Baby Vegeta by miles. Background, motivations, etc. were on point. Comparing plot holes between GT and Super is like comparing apples and oranges, but the writing during the Baby Saga was very good imo. Created a believable villain who you can easily see their side of things. However, this doesn't sacrifice anything in terms of Baby's character, as his personality and the way he goes about his revenge still allows you to cheer for the actual protagonists in the story. Shows sometimes make the mistake of making the villain too likeable, to the point where people would cheer against the hero.
Goku Black is a mess. Complete megalomaniac who has very thin and truthfully, shytty ideals and motivations to do what he does. He is nowhere near charismatic or nuanced enough to mask his failings as a character, so it just comes off as forced. His eventual reveal of being Zamasu killed a lot of his initial hype and mystique. Hell, his plan of taking Goku's body was stupid as fukk in both the anime and manga
. Anime, just because Goku was stronger than weak ass Supreme Kai was enough for him to be like "Let me use these Omnipotent Wish-Granting Spheres that could give me literally -anything- and steal this mortal's body." Manga, he switched with Monaka first, then switched with Goku
Didn't switch with Beerus, who he actually knew of and whose power was confirmed, but switched with some alien from a backwater planet who he just heard of in passing.
Hell, he could have switched with Zeno
Goku Black's story needed an entire rewrite if we keeping it a stack.