I have no personal experience with summer internships--I'm probably just going to do research at my college over the summer and hopefully get on the payroll. I'm working w/ one of the professors now.
But to answer your question, I don't know that one is better than another. Unless you're working w/ a Nobel Prize laureate or something, I really don't think prestige factors that much into it. I think it's more of what you get out of it--potential connections, research experience, $ , and hopefully some friendships.
This is a really good list of summer undergrad internships:
http://www.care.ucla.edu/inside/intern.html
Some of the links are outdated, but you could google the names of the programs and get to the sites of interest.
A lot of programs are 8-weeks (so probably about 320 hours), full-time. One of my relatives did a summer undergrad biomedical research program at Iowa. He earned a pretty decent stipend. I think he had the choice of $2000 + room and board or $3000 w/o room and board. He also got 3 credits or something out of it. He thought it was an excellent experience.
I know another person who did this same program, different field, different year. It turned out that he worked with one of the professors who was on the U Iowa med school adcom (he didn't know this at the time). He impressed the prof he worked under and had a pretty solid app too. He might have been accepted w/o working with the prof, but it certainly didn't hurt him.
😉 For this reason, I would try to find an internship at the med school I'm most interested in. Even if the prof you work for isn't on an adcom, he/she may be well respected by the university's adcom members.
You can find similar programs just about anywhere in the country.
In addition to biomedical research programs, there's a lot of clinical internships at hospitals too.
Phil
ps you posted in the postbac forum, just so you know, a lot of these programs are require that you're an undergrad so postbac students might not be eligible (that's why I'm probably just going to continue research at my school)
