Hmmm... good question.
I really like the style of Sims 4 in general. I like the bright colours and I think the FX team do a great job of making the worlds really beautiful. I prefer Sims 4 sims to any other because of the realistic bone structure and the diversity I can give them.
TS3 could look really beautiful too, and I did tend towards darker terrain and lighting/water files. I liked when the worlds looked quite realistic. But I prefer TS4 sims.
My only complaint is that some TS4 objects can be lacking in detail, and I'd prefer a bit more shape to the meshes (some can be very boxy). The upside of this is that they don't create as much lag. I think this is improving as the game progresses though, the more recent content seems more detailed than the earlier content.
It would be nice to see some darker themes sometimes, maybe a world with grittier less cartoony colours for a bit of diversity. But in general I'm happy with the art style of TS4.
I think both games have their positives and negatives.
