I'll go ahead and echo some of the previous sentiments in this thread and say that while there is definitely a "research" vs "practice" distinction, it is pretty inconsequential in my opinion, especially at the master's level.
If you were 100% sure you wanted to pursue a PhD, it would probably be good to go for the MS, but not because it would necessarily give you a huge competitive advantage (if any advantage) in the admissions process but because the material you'd learn would probably go a little deeper into methodology and theory, which would be helpful when studying advanced biostats.
Similarly, if you decide to have a more practice-oriented career, I don't think having an MS instead of an MPH would really hinder you.
At my school, my option was between an MPH and MSPH in epi. Although I think I want to continue to a PhD, I opted for the MPH simply because it was several thousand dollars cheaper and I didn't think the cost difference justified getting a basically equivalent degree. That being said, there's probably a greater difference between an MPH and MS vs an MPH and MSPH, but I still view them as largely equivalent degrees at least in terms of career trajectory or PhD admissions.