You cant really go wrong with either of them.
I have 2 NT1a mics and I love 'em! I have done several recordings of Classical Harp and the NT1as sounded incredible on it.
The NT1as have one of the lowest self noise ratings for their price range and this is particularly useful if you are recording a very quiet instrument (like a harp) because there is less "circuit noise" from the mic if you crank the gain up (obviously, this is also affected by the quality of the preamps on your desk).
I have read in some magazines that the two models do have a slightly different sound, and that they reccomended going for the original NT1, but this really is a matter of personal taste.
That said though, you cant really go wrong at this price. Both models are great mics.