If you want to do research, the PhD is the way to go. Getting a PhD consists primarily of doing research, and is the prerequisite for doing a postdoctoral fellowship, a faculty position, and many industry research positions.
I would recommend looking at PhD programs at a few schools--you'll want to apply to a few, and sometimes going to a different graduate institution can help expose you to new mentors and ideas--and seeing which programs and faculty members you'd like to work with.
You can also talk to professors or graduate students at Case about their research. They will also know professors at other institutions who do similar work. I would very highly recommend trying to do a research project with a professor or graduate student at Case, as this will be very good preparation for a PhD program.