yea i meant internal medicine. Mind you i am going to be a first year DO student in a month, so all my info is people on this forum and asking friends who went through the match. I know they are couple of residents on this forum.
Both residencies will make you an attending after its complete. The only difference is
1) you get to be

and working at harvard or something
2) the research opportunities are generally better, which comes to play for a fellowship when you apply to cardio vascular or something. That doesn't mean if you are a resident at Joe Shmoe hospital that you cant get it. It might be easier specializing in cardio, GI (if your IM) etc because of the more research opportunities which lead to you getting published. Usually the more difficult residencies are academic residencies and not community residencies
3) The rec's you get for fellowship will generally be from more respected physicians in their feilds if you did it at a big time residency. But you still have to impress him/her just like you would in a community hospital.
I am sure there is more, feel free to chyme in
All in all you can get a fellowship, if you work hard, impress people, but top flight programs have some advantages. It is not the end of the world if you dont get in.
I think around 3 percent of sgu grads, got gen surgery so it is possible