I think it totally depends on what you are looking for and what you like. Having done a private practice internship and specialty internship, I know that many private practices often have a higher caseload and things happen more quickly. There are no students to teach but often little time/limited resources for you to work on furthering your education (ex- writing papers, access to journal articles). I would still do these internships again in a heartbeat. I loved them. Now that I'm in an academic residency, things are very different. Caseload is lower but things go MUCH slower- everything has to go through 3 layers- student, resident, faculty. I'm responsible for working on cases with the students and havng rounds with them every day. However, I am given time to work on my research, have access to an awesome library and know that all my residency requirements will get done. Some people feel that the university setting is made more for teaching while private practices main goal is making money. Sometimes I do agree with that statement....not always.
It looks like you still have some time to make choices though. I would do externships at both places or at least visit. Try to make contact with the current residents and see what they have to say- they will tell you the truth!
Hope this helps a little!