This is how I think about it:
There are 10-15 brand name programs that everyone acknowledges. Sure, people may debate which is #11 vs #14, but in general these programs are considered elite programs. Check out the rankings thread. As subjective as these rankings may be, you'll see that the same programs are universally mentioned within the top 10-15 spots. In terms of doing aways, most of these programs will have many rotating students at them and it may be harder to "stand out". That is not to say that one should not do a rotation here; a strong letter from a big name at one of these places may go a long way.
I believe every other program is a solid program in radiation oncology. They provide excellent training but may not have as many research opps or may not have all the toys that some of the elite programs do. I feel that an applicant can get the biggest bang for their buck by doing an away at programs like this. You may not have insane amount of competition from other med students, and you may have a more personal experience as a rotating student. Most of these programs will offer rotaters an interview, whereas there might be less of a guarantee at an elite program.
While there may not be any low-tier programs per say, I think newer programs or unstable programs may fall into this category. I would shy away from doing an away at these programs as your yield may not be great.
Just my two cents.