Thanks for the response I have to make a decision by 15th April
Machine Learning program is definitely the main concern, but the thing is both the universities have a great faculty for their ML track.
GaTech has Mr. Vempala, Mr. Chau, Mr. Gray and Ms. Park. On the other hand Columbia has Mr. Vapnik (the inventor of SVM), Mr. Jebara and Mr. Hsu. The faculty is great at both the universities, at least as far as I know. However, if someone thinks different, I am all ears.