I prefer retail right now. I don't think classic is a bad game, but I don't want to play the same game I have played a lot of years ago. I feel it very old also. I prefer the new content retail has, although I think it could be better.
The only thing I think it is better in classic it's that classes feel more like they are the same class no matter which spec you're playing. Now some specs makes the class feel so different than they look another class rather than the same.