In my opinion as an MSII, take the publications. I've been in one of those great research labs that I've thoroughly enjoyed but have not gotten hardly any pubs out of it. Even though I love everybody I work with, if I had to go back and do it all over again I would strictly choose publications over the quality of the lab.
I'm thinking of applying to residencies in a few years, and people don't give a crap how much you liked your lab and how much you learned there. They want to see results. The number of publications is important.
To me, it's like asking if you would rather take an A and not learn as much, or get a C and learn a ton. Tough call, but I'd take the A, as it may open doors for you in the future. A grade of C may slam doors for you, no matter how much you learned.
Anyways, ideally you'd get in a lab with a bunch of pubs and great research, but if it's not the case choose the pubs. I've heard many medical students whining about not getting pubs, but I haven't heard a single one whining about not liking a lab they are getting 5 pubs from a year.