As @Metawampe indicated, unless you are truly in love with the Columbia Core- and are strong across the board academically- Columbia as a Junior is a bad idea if you are truly set on pre-med.
yeahhh…so from here it looks more like a straight prestige-name play, as there are quite a few places between Rowan and Stanford with “high quality resources”, so I am wondering if you are suffering from the common (but erroneous) belief that a fancier name will help your chances in med school apps?
One challenge with transferring as a Junior is forging relationships with profs. It is do-able! but you are starting on the back foot, as many research posts for the coming year will be already filled by existing students. You will have to establish yourself as a star to get the kind of LoRs that you will need for med school.
I would drop Columbia, Cornell, Stanford and the UCs, keep UPenn, NU and Vandy, and add UNC-CH, UVa (both of which are state colleges but meet need), Pitt, maybe University of Richmond, maybe a couple of others.