¿Weka vs scikit-learn/NLTK?

Im in the process of selecting a tool for natural language processing/machine learning/sentiment analisys task in spanish. By the way , could anybody help me to convince to my thesis advisor why scikit learn is better than Weka. I need some factual data, features on why scikit´s better option than weka, i argued that productivity is a nice feature of scikit-learn but my advisor didnt like the argument.

Thanks