Hofstra MS3 here to add some perspective. There are several categories OP should be considering right now, and I will break down my opinion on each of them.
1. Name recognition: There is no getting around the fact that Mount Sinai has a near-impeccable reputation, while HNSLIJ's reputation is limited. Among new schools there is probably the most buzz about our school as it is in the NYC-area and our leadership has done very well hyping us up. We have also done well above-average thus far on testing (Step 1 and shelf exam scores consistently above the national average), which despite everyone agreeing is a crappy method of comparison, we were all waiting for with baited breath. Not to be undervalued is the reputation of North Shore University Hospital and Long Island Jewish Medical Center. Aspiring medical students don't even realize that Zucker Hillside Hospital (LIJ campus) is one of the top psychiatric facilities in NY and Cohen Children's Medical Center (formerly the Schneider Children's Hospital of NY, also LIJ campus) is probably the best place to go for pediatric healthcare other than Morgan Stanley (NY Prebyterian//Columbia). So while Mount Sinai clearly takes the trophy here, it's not like comparing a Ferrari to a Fiat, it's more like comparing a Ferrari to a BMW.
2. Location: This is another round I must concede to Mt. Sinai, although I would make a similar comparison to above, as we're not out in the country, we're just not within the limits of NYC (by about 5 miles--LIJ is actually half in Queens and half in Nassau County). People like to complain a lot about Long Island, but in reality, I have classmates who live in Manhattan, Brooklyn, and West Queens; it's doable and becomes even more reasonable 3rd year.
3. Research Opportunities: This is where I am going to have to break away from the mold and make a heavy claim that research opportunities at HNSLIJ are, to the best of my knowledge, comparable to those at an institution like Mt. Sinai. A lot of responses will follow in which people call me naive or an idiot. What these people fail to realize is that NSLIJ is a massive health system (1000s of physicians) and while its entire faculty may not be as decorated as the faculty at (as an example) Mt. Sinai, there's a large number of academically-oriented faculty here. The flip side of the coin is that we are talking about research opportunity, which implies not only that there is research conducted but that you may participate in it. I am going to go out on a limb and suggest that we have simply the most receptive faculty to taking in medical students for all purposes, including research. I recently decided to apply to a competitive specialty and realized I could stand to bump my application with some clinical research. I was shocked at how easy it was to get myself involved with multiple research projects. Sometimes I haven't even had to ask, I've been asked by residents and attendings to join. And I'm not even that research-y, although I'm trying to reinvent myself that way.
4. This contributes to #4. I can't overemphasize how nice it is to be literally a part of the health system, and it hasn't even completely sunk in with all of the faculty and staff yet. We rotate exclusively throughout this health system of which we are a part. We have the same ID cards, the same white coats (albeit shorter), the same facilities, heck I even clean my white coat in the in-hospital dry cleaners that the residents and attendings use. And I recognize a ridiculous portion of the people I pass by in the hall. Granted, this comes with the major downside of not experiencing other health systems during clinical rotations, which some students may view as a disadvantage. Having lived through it and interacted with many other medical students from other programs, I can safely say I prefer it this way, though that may not be your preference. I'm not sure what this is like at Mt. Sinai, so I can;t really comment on one vs. the other.
5. You don't even realize it yet but when you get to the attending level it's much more of a regional game. My attendings trained at all the big city programs so that's where they have connections. Many of them even trained (as residents) faculty who are intimately involved in the residency programs at places like Cornell, Columbia, Mt. Sinai, etc. They are very well plugged in, and we are plugged in to them, so we benefit as a result. I will be asking the division chief, associate division chief, and perhaps the department chairman (who, for what specialty I want to do, sits on the ROC) for letters of recommendation--all of whom I know very well because I see them several times a week and have been able to take elective time in their department. I'm not some crazy ridiculous med student either, I've never published (yet!), and I'm not going to get AOA. This is a common occurrence among my classmates. Again, I'm not sure how it is at Sinai, I'm sure there are students who are similarly well plugged in, but I have the distinct impression that it is much more commonplace here. This gets back to #4, the sense that we are all members of the health system, no matter how junior we may be.
6. I can't really help you much with class structure; if it's your prerogative not to attend class, you shouldn't come here. I thought it was amazing that we only had 4 hours of class M/T/W/F and no class on thursdays for our first two years; I would never not go to class in med school, learned that lesson the hard way as an undergrad, plus you're paying for it. If it helps, out classes are not like normal classes, we do some lectures but the remainder of the curriculum is case-based and more conducive to "self-directed learning" which is what I assume you mean you want when you say you don't want to go to class. My classmates who didn't have great experience with PBL tended to want more lectures, not the opposite.
7. Don't know what they're brewing up at Sinai in this regard, but our school is really one of the pioneers of early clinical exposure, which I won't get into (there;s plenty of HNSLIJ propaganda about that out there), but I will tell you was an indispensable part of my learning.
8. Our Dean, who is also Physician-in-Chief of NSLIJ, was formerly the internal medicine residency director at Mt. Sinai.
tl;dr: I have no clue what's really important to you. Realize that the major advantages of Sinai over Hofstra are location and reputation. I urge you to consider that while we are certainly nowhere near as prestigious as a place like Sinai, we are not a second-rate medical school, and are beginning to be thought of highly. So if you pick Sinai over Hofstra for its reputation, do so realizing you are picking a top-tier school over what I would (with much bias) call a second tier school, which is a totally legitimate decision. But don't rationalize it by saying that Sinai's a better choice for academic medicine (false), Sinai provides more research or any other kind of opportunities (false), HNSLIJ is a lower-tier school (false, by the numbers at least), Sinai is better supported by its hospital (false), or any of the other garbage people have been saying. If Sinai's reputation is worth the extra $ to you, I don't blame you. You have two excellent choices before you, and to get that much $ you must be very bright, I wish you the best. Remember that wherever you go, you're going to be a doctor, and that's awesome!
