I realized that I know groups with distorted cyclic subgroups and groups all of whose free abelian subgroups are undistorted, but nothing between. Maybe it is a naive question, but:
Does there exist a group $G_n$ all of whose free abelian subgroups of rank $\leq n$ are undistorted and containing a distorted free abelian subgroup of rank $n+1$?
The case $n=2$ seems to be already interesting.