Both academic and private practices love to hire known quantities - that translates into academic practices disproportionately hiring their own fellows or residents over outside candidates. If you have your eyes set on a specific institution, your best bet is to do a fellowship there (fellowships are generally much easier to get than residencies) and be a rock star (i.e. hard-working, detail-oriented, and perhaps most importantly, easy for everyone to get along with - pretty much all groups will prefer the hard-working and pretty good fellow who everyone gets along with over the genius fellow who ruffles feathers with a few attendings). Even if there are no job openings in that practice at the time you graduate, when an opening eventually pops up in a few years, if the attendings really liked you, you'll be at or near the top of the list for new hires. I have many colleagues who have become attendings even in big name academic medical centers in coastal cities this way. I myself got in this way as well into my current group, which I would have otherwise had no shot at if I wasn't a known strong candidate.
In general academic practices are not as competitive to get into as private practice in any given location; it seems that the trend is for rads to start out a career in academics, then eventually transition to private practice after some years of experience.
