My Y is currently at Tesla getting some delivery day items fixed. In the meantime, I have been driving my 3 before I sell it next week.
The 3 is definitely more sporty feeling to drive. Everytime I get behind the wheel it feels like a rocketship sports car. The handling is better and it really is a fun car to drive.
That being said, and this is a personal aspect, I find myself driving a bit more aggressively compared to the Y. Knowing I have that power and handling makes it easier to overtake someone or take that corner just a little bit faster than normal. It invites you to push the envelope because it is absolutely capable of handling it, which means its easier to get into trouble with.
With the Y, the car still has that acceleration that makes a Tesla great, however the urges mentioned above are tamed down a bit. Between that, the increased ride height, the quieter ride, and the loads more usable space, I am extremely happy with my move to the Y. In a perfect world I would have both (or the Y and the roadster... A man can dream).
Note: These are my personal experiences. I understand that we all have different driving habits, experiences, preferences, etc. Merely sharing my personal experience/thought process owning both vehicles.