I play ts4 a little. It is true that the movement is more fluid (except for that annoying auto-adjust thing in middle of rally) and the look is more fun looking and contemporary. It even has a Williams sister and Djokovic. Those are all pluses in my book. The thing that TS4 doesn't seem to have is realism. TS3 was not the best game in the world as the movement was not the most fluid and had a high learning curve which alienated many new comers. It almost alienated me. I remember throwing my controller down in frustration a couple times, lol! The game stands the test of time though. I was astonished to be learning new things about the game 3 years later. I currently get bored mid-rally sometimes in TS4. I catch myself saying, "When will this rally end?" lol!
TS3 is quite deep indeed. There are still shots I don't know how to do. I voted TS3. An overall excellent game that I hope 2K sports builds on in the future.