I think it depends on a few things:
1. will the app always have a view of satellites (if not then use location manager as it uses Cell towers).
2. How important is positional accuracy (i believe that GPS is more accurate, but am not completely sure)
3. or you use both:
a. Use GPS when a signal is available and the accuracy is good.
b. switch to location manager when no GPS is available. (in your position log you could annotate if it is from GPS or Location manager source)
These are just my thoughts,
I hope it helps
Stu