I highly recommend the New England Journal. Their reviews are excellent, as are their case reports and weekly images. Reading the table of contents alone, believe it or not, can make you look good on rounds just because you can say "there is a new NEJM paper out on blank." Many schools get online access to the journal of free....I would check to see if your school does.
JAMA is often offered for free by joining AMSA, but is much more variable than NEJM in quality.
The AAFP journal is sub-par in my opinion.
-PB