I think MIT is probably the best choice. It will be grade deflating, it will be tough, and it will be competitive, but you'll come out better for it on the other side. Iron sharpens iron, and the iron up in Boston is some of the best in the world. That's not to say going to any of the other schools will tank your chances. It is true that you can go anywhere from anywhere (in theory). At ASU you could probably have similar achievements, but you'd have to be very ambitious, self-motivated, and driven to carve out opportunities for yourself - opportunities that would be served up on a platter at MIT.
It honestly depends on what you think your goals are. Just to offer an extended metaphor, say that you want to become a sushi chef, and you have to choose where to shop for fish - a Whole Foods store in Iowa, or the Tsukiji fish market in Tokyo. You know that you'll study hard on proper technique either way, and both results will probably taste good. Whole Foods has high quality products. But if you want to be the next Jiro Ono and are hungry for michelin stars and culinary accolades, you know where you're going to have to go.
MIT provides exceptional training; the quality of the faculty, your peers, and research opportunities there cannot be overstated and will really set you up to be a leader and scientific innovator in medicine. The name of the institution, and the names of the faculty you train with will provide a considerable advantage with elite programs (if you're curious, take a look at the facebook accepted student pages for T10 schools - there's always a sizeable MIT contingent. Definitely selection bias at play, but still worth thinking about).
If you have no interest in academic medicine or research and want to be a family practice/private practice doc somewhere in middle-America, then these advantages aren't really going to be helpful. And do what makes you happy, but honestly, if you're a strong enough student to get in, you're pretty smart and have already benefited from many top opportunities - we as a society need your "wicked smaht" brain in medical leadership and innovation after receiving the best training possible. I'm also of the opinion that it's usually preferable to go with the "bird in the hand". You worked hard and were exceptional high school, and earned a rare boon that provides career advantages ranging from minor to major. You can cash that out, or you can pass on it with the expectation that you don't need what it offers. Life is unpredictable so I'd personally rather have access to that boon - let's say you turn to the dark side and decide you want to go into tech/IB/consulting/PhD where prestige/being a recruiting target is undeniably crucial - then you might really be kicking yourself for not having access to that advantage.
Of your other choices, UCSD is also very strong - just a bit behind MIT. They have a strong BME program+faculty, a top medical school+faculty, and SD is a hub for the biotech industry. So they're a very solid choice. BU, CU Boulder, and UT are also solid schools and you'd be fine there, but I don't know if the training would be exceptional. But there could be other decisions at play. Let's say your family is all in AZ and all your friends are headed to ASU, so that's where you really really want to go. Then it'd definitely be understandable to go for ASU since it would be a major quality of life advantage. Or maybe you love Texas. Or maybe you love skiiing or the mountains. Alternatively, if you'd have to take an unreasonably large amount of debt for MIT (not just extra expenses, but more like >40k in loans) it would probably be good to go elsewhere.
