Congratulations on your acceptances. Properly weigh your options and your reasons for liking/not liking the schools. Not wanting to be a guinea pig doesn't mean you want to be spoon fed. Talk to med students, residents, and physicians (preferrably more recent grads) about what are realistic indices and signs of success at a med school. (in other words, how do you know you will be successful at the new school?)
I've tutored M1s and M2s who started med school with great GPAs from college, all-stars, go getters, and student leaders in college, who failed a class or two because of significant curriculum changes (at an established med school). I can only imagine what their experience would have been like in a brand spanking new school.
Yes, residency programs care about board scores a lot. At a brand new school, if the class doesn't do well on boards, that failure still falls on the student's record - and bites them in the arse when it comes to residency application season. Whether or not it was due to the curriculum.
Personally, I hate spoon feeding. But when it comes to medical education, I would rather know what I am getting into before I dive in. I'd rather know a school's record on board pass rates and residency match history. To me, not having these (and not being an established school) are deal breakers. But maybe not for you. And maybe being a self-learner will get you by... but chances are that's not you.
A way they can make up for not having that information is by maybe offering a free or discounted subscription to UWorld, and access to academic support in case their curriculum doesn't fit my learning style.
They can maybe make up for the lack of residency match history if they recruit faculty members who trained in different geographical regions and have academic connections there. They can establish relationships with teaching/academic hospitals to send students there for rotations. These give you a chance to collect mentors and advisors who have ties elsewhere and are willing to write a letter for you. Etc etc etc.
Find out why the school has decided on the curriculum it has. Check how the new school plans to handle the first two years, step 1 and step 2 ck prep, core clinical rotations, and opportunities for away rotations and/or independent student projects. Talk to medical students and residents, compare this to their experience. (The reason I don't say talk to physicians here is because medical education has changed quite a bit in the past 10 years and it might be an apples to oranges comparison).
The fact that the "low tier" school is a state school makes no difference. You believe you will be successful at the new school, but what makes you think you won't be successful at the established school? They are both essentially "low-tier." Get past the "low-tier" status. What's more important is, are the students happy? Med school is draining - will you have a support system while there? What's their average step 1 and step 2? where do students go for residency, and in what fields? how did last year's class do in the match? do students make time to do activities they enjoy? How does the school approach communication skills, professionalism, systems based practice, etc etc all those core competencies?
It's a tough decision. But you have a good problem. You're going to be a doctor. Talk to your mentors. Here on SDN, we don't know the whole story and we don't know you. Talk to people who know you and can help identify what is best for you.