I have heard of AUC. They are typically considered in the "Big Three" when people refer to Caribbean schools, SGU and Ross being the other two. Depending on who you talk to, SGU is considered the "best", while others say Ross is "best". These two schools in particular have good clinical contacts in place, and students tend to get good residencies. "Best" is, of course, a relative term. Both offer advantages and disadvantages, just like any school. Again, I can only attest to SGU.
As far as being equivalent to a US medical school, I think the quality of the Basic Science education (the only time you spend in the Caribbean--unless you want to do some clinical rotations there) equals or exceeds that of other US schools. Again, I don't know for sure, but our first time USMLE Step I pass rates are usually around 90%. We also get guest lecturers from around the United States, Canada, and UK who are quite good. Some have included attendings at Ohio State University, Weil Cornell Medical Center, Harvard, University of Toronto, and University of Rochester to name a few. My cousin graduated from SGU in May, and while on interviews for Residency, he was told by more than one program director that SGU is "not really considered a foreign medical school." The fact remains, however, that you ARE from a "non- U.S." school, and that may factor in when you go to choose a Residency program. Step I scores are very important in this respect.
So, SGU is eqivalent in the sense that we have some good professors (and some not-so-good ones), have a really nice campus, use many of the same text books, and do our clinical rotations right along with other US medical students. We're different in that we have a few extra hurdles to clear before attaining licensure, and still tend to have that stigma of being "forced" to attend a school in the Caribbean because we "couldn't get in to a U.S. School". This view is fading, but still remains among certain people.
Hope this helps!
Brian