My daughter is a Neuroscience major at Midd, and my nephew is a bio major at UCLA. We are from Chicagoland, and they are from the LA area.
Both colleges have research opportunities, however they are different. For lab experience at UCLA, one must be more proactive, since you will be one student out of dozens or hundreds who are taking that course from that professor. So it is unlikely that the professor/PI will notice any one student from the class itself, so you would need to go to a few office hours, ask to speak with the professor, etc. In short, you would have to do your schmoozing mostly outside of class and the lab.
On the plus side, there will be more choice in labs.
On the other hand, at Midd, you will be in a small class, and the professor will know your name in a couple of weeks. Asking about research opportunities will take very little effort (but standing out may take more - se my remarks below)
As others have written, the nature of your work will differ. The work that you are more likely to do at UCLA will be in the more technical aspects, while at Midd, you are more likely to be engaged in your own research. On the other hand, the lab facilities at UCLA will be more extensive, so your technical work will involve the use of more advanced equipment.
However, it is not absolute. Some PIs at large universities are really good at encouraging the undergrad research, and you can join these labs as a lab member. On the other hand, internships are readily available for Midd students who want to work at a lab in a research university. My daughter will be having her second internship at U Chicago this summer. She is working at one of the top labs in the field.
Regarding the Cons for Midd:
There is, in fact, sometimes too much partying, as is true for all rural LACs. The lack of a Greek life does not hinder that in the least.
There is no social gap between athletes and non-athletes, but mingling is limited by the fact that athletes have to build their social life around their training and game schedule. The mingling between athletes is also limited because different sports have different training and competition schedules. Volleyball and Skiing will have very different schedules.
There are 787 varsity athletes of around 2,500 students. So a bit fewer than every third person is a varsity athlete. There are also club sports, as well as many outdoor activities. It is an outdoorsy campus, and sports are part of it. Some of those sports are, however, very geeky, like ultimate Frisbee or Quidditch.
Regarding the cons for UCLA:
Quarter system can be a good thing
You will be as big a fish at UCLA as you would be at Middlebury. Academically, they are equivalent.
In some ways, at UCLA it will be easier to stand out, if you make the effort, since most students in large classes will not try to connect with the faculty teaching the class. At a small school, the professor know everybody, and everybody meets with the professor during office hours. So you have to do more than that to stand out. At a very large school, not being intimidated, and not being uncomfortable with standing out, will make an impression, so simply going to office hours and having an interesting discussion with your professor will make you stand out in a positive way.
Course registration is difficult everywhere in some majors. This is true for any college which is not suffering from a drop in enrollment, which is not the case for either UCLA or Middlebury.
I will disagree with some others on the thread. While there is access to good hiking trails in UCLA, the campus itself is urban, and access to outdoors will be restricted to free time. At Middlebury the colleges itself has outdoors. Being able to walk to the Knoll at night and see a sky full of stars is not an experience that one can really have at UCLA. The air is also cleaner at Midd…
Of course, UCLA has the amenities of a major metropolis.
For you specifically, I would actually recommend Middlebury. Not because it is objectively better, nor do I think that either is better for you academically. It is that you have grown up in a major urban area, and I think that you would really enjoy being in a more rural location for a few years, especially one as beautiful as Middlebury.
Whatever you choose, I am sure that you will do very well, and have a great time.
Congratulations, and good luck!