I prefer the old one too! I know the artwork always had that vectorized look but the newer feels waaay too... clean, too soft. The team involved also makes the Rythm Heaven games, right? I don't like how it pushes it way too much onto that art style.
Like Chance said the rough feel to it is a lot more unique
Something that sort of bugs me is when developers start forcing relationships between 2 series that aren't really related aside from same developer and especially when it's abrupt. WarioWare and Rhythm Heaven being the example here. Sonic and Puyo is another I can think of. I mean it can be helpful for like more exposure but I guess crossovers in general bug me
The classic artstyle is what I identify more as being WarioWare. Although I don't dislike the new one, the classic has a rushed vibe to it which kinda fits both the goofiness of the games and the general plot of Wario making a game. Plus the characters match more to Wario's design and the new one, Wario is still the same and feels a bit off compared to the rest of the staff now.