How do you expect the selectivity of these programs to be compared? I mean, I don't think anyone here can give you a realistic answer spanning all of the Astrophysics and Statistics/Applied Math programs. It could be different for every school. Apply to the places where there is research interesting to you (regardless of the field) and go from there. It isn't worth your time debating this question unless you've picked out a specific school and someone from this forum has experience with both of the departments, which is very rare.
With that being said, I see no particular reason why a physics student should have trouble getting into one of these programs as long as they have a decent math background. For most of the programs, the Math GRE is probably required.