It mainly depends upon the stream you belong to. If you have more technical grip then go for Data Science, if you have more of management and speaking skills then I'd suggest choosing BI.
Some universities have begun providing DS into masters than be a little bit cautious. Do some research about the type of DS projects did by university alumni, know the expertise trait to be assigned professors, etc. If you are a beginner and want to know more about Python and R programming language then do refer the following video tutorials:
You can get a hands-on project by referring to the Data Science course by Intellipaat which will teach you Data Science from scratch to advance.
And if you are more into videos then do check out the following video tutorial which will help you in mastering in the field of Data Science:
If you want a detailed explanation of Data Science then do check out Data Science tutorial which will help you in understanding DS.