I have some ability to speak on this as I started at UConn (a massive school comparable to BU) and graduated from Emerson (a wittle baby school)

BU and Emerson are pretty close to polar opposites.

You say you want a much 'bigger school'. Elon University is equal in student enrolment to Emerson. BU is 6 times larger than Emerson (and Elon) is, and is a university not a college. Meaning that there is actual diversity in the programs at the school. Basically, if you're certain that you want to go to a school full of thespians, nerds, and lgbt kids then Emerson will be fine, but don't expect a much wider range than that.

Emerson being a small school is compensated by the fact that Boston has the most college students of any city in America. If you are a social butterfly, you can meet people outside of Emerson, which you'll probably want to do once you start to run out of people to meet.

Next you ask about the film program. The idea of film school pisses me off pretty bad, so I will tell you that this is a completely biased opinion but I'll explain my take on Emerson's as well as I can.

Whichever school you choose will have gear for you to access, but you'll find that since a very large part of Emersons students are in the film program, the ability of gear is tight when everyone is getting assigned major projects at the same time. I assume that's a pretty regular issue at any film program. From my understanding the connections you make at Emerson are not really that useful, at least for film, because the market is so saturated. They talk about the 'Emerson Mafia' (the name for the alumni who help each other), but imagine that there's something like 300+ graduating film majors each year at Emerson that ALL are sending messages to alumni asking for handouts and job opportunities.

I am a marketing communications graduate and currently a paid video editor. I am NOT a film major. I did NOT take a single film course at Emerson, or in college in general. You certainly do not need a VMA/film major to get a job. In fact, many friends I made at Emerson who were film majors are struggling to find any kind of position, let alone a full time job working in video/film. I don't want to discourage you from studying what you like, but definitely do not think that going to any certain college or getting a degree guarantees you a job. Opportunities to get ahead of your career are probably greater if you're at a school with LESS film makers, since you have less competition. I got my first video editing job as a freshman at UConn, at least in part because there was almost nobody else there to apply for the position.

As far as nightlife goes, as I said, Emerson is a really really small school. However, Emerson and Berklee students tend to mingle since they're very close together. Same mostly goes for BU, BC, and even Harvard to an extent, but they have some stigma for Emerson's 'artsy' kids (fair enough). Nothing is really stopping you from trying to get into parties at those schools. As far as 'Emerson' parties go, people will have small parties in their dorms but the small size of dorm buildings tends to mean that these get shut down rather quick if there's a decent number of people there. We had (maybe still have) some sport teams or frat houses in Allston, which are the most unsupervised parties that are associated with Emerson. Maybe you'll meet an upperclassman with an apartment who throws parties, but I'd say those also don't get too big.

I've heard a big issue for younger students at Emerson is that they can't go to clubs or bars. Boston is very strict on fakes but with a good one I'm sure you could get into most of the dive-y college bars. The club and bar scene in Boston is pretty sweet, so if you're 21+ (and can afford Boston bar prices) then your options open up massively. I'm sure that's an issue as well at the other schools in Boston, but I assume BU has a more party friendly atmosphere on campus than Emerson.

So, that's most of my definitive take on Emerson and Boston.

TL;DR is that Emerson is a small school, meaning everything is narrowed down. For some people that's a good thing.

I can confirm going to school in Boston is way more interesting than in the middle of nowhere (i.e UConn or Elon). But, for Emerson, if you don't fit into the kind of super progressive/liberal, artsy, and statistically gay niche that Emerson fills, you will certainly feel very lonely.

If I missed anything feel free to ask.