I'm accepted by both programs and I definitely prefer MSR.
I think MSR put more weights on research, and more important you will get funding from RI professors.
It's also about your research interest. I'm a vision and robotics guy, so MSR is better from me. If you prefer DS, DM or NLP, MCDS might be a good choice.
I think the changes in the Research Area and PoI shouldn't be a big problem.
Fact is that my Research Area is always changeable ever since I submitted my MSc application form.
And I got an interview yesterday. So be relaxed.
Shouldn't be a big problem if you have strong connections with POIs, e.g they know your recommenders.
Honestly, I think GRE is the least important among TOEFL(if needed), LOR, GPA and Research.
However, I heard if there are too many applications they may use English score as a filter.