I’m a Junior in high school, double legacy at Penn (Hispanic if that matters) and am considering applying ED. After visiting several times I have gotten a generally good impression of the school; I love the campus, the closeness to the city, the academics, etc. The only concern that I have is that I might not fit in socially. I’m super super shy, don’t have any interest in partying or Greek life, and have never been very academically competitive among classmates. Besides Penn, I have looked at smaller liberal arts colleges that have a less competitive atmosphere (example: Vassar, which I really love). Going to an ivy league is not a priority for me, but I do want to go to a school with a lot of great resources that could help me get into a top law school. I guess my question is… is it a good idea to apply ED at Penn? Is Penn a good fit for someone who is sort of shy and not very competitive?
It’s only a good idea to apply ED to Penn if you’re absolutely sure it’s where you want to go. It’s true that your legacy status is only a ‘plus’ in the ED round, but that’s not a reason to apply if you’re not totally sure you are committed to Penn. No matter what hooks you may have - it’s not a help if you don’t really want to be at a school. Should you decided Penn is THE PLACE for you - and if the finances work out - by all means apply ED because that will give you the best chance for a YES. But if you’re not sure or if you think that another school would be a better home then don’t apply ED. If you’re only applying to Penn (or any school) to get a leg up on law school - I don’t think that’s a good reason to apply ED or RD.
Penn is a big school - you can basically make it as small as you want. I don’t think being shy or being ‘not very competitive’ = poor fit. Can you advocate for yourself? Will you take advantage of what’s on offer? Those are the more relevant questions. It’s true there are fabulous resources at Penn, but there are fabulous resources at many schools big and small.There’s a LOT to recommend Penn. Heck, I’ve been doing alumni interviews for years so clearly I’m a fan. Still, Penn isn’t right for everyone - even people who are legacy.
FWIW, Greek life is certainly present at Penn (I think the campus is 30% Greek) but it doesn’t dominate the culture the way it does at some schools. I don’t think that will be an issue for you. At some schools, that is the case - even where the percentage of students in the Greek system is less than 30%. It’s something you’ll want to research no matter where you apply.
You could always save Penn for law school. 
I can’t imagine that someone super super shy would make it as a successful lawyer or even survive law school. Perhaps the time has come for you to overcome the shyness. Assuming you’re admitted to Penn you can dial your social persona up or down as much as you choose. Hopefully you’ll choose dialing it up.
Penn is a big school, and IMHO, people of all sorts do better at a big school where it is more likely to find someone like them than a small school where there is a smaller population and smaller classes.
Greek is less than 25% at Penn, and although there are parties, they are not a focus.
Penn has AMAZING resources, so if you want an interdisciplinary education in any way, it is far easier at Penn and other schools that let students take classes across the university. Like, an engineering student can take a Wharton class and a fine arts class with no issue (harder to change majors though…).
I didn’t think Penn was hyper-competitive, and I even dated a guy from Wharton. All the “competitiveness” is mostly from the outsiders looking in. Yes, if you must get a 4.0 GPA and you must be a biophysics major, it will be tough. But I do not think it is that competitive as in people actively trying to sabotage others or bearing ill will against anyone with an A in a particular class.
I suggest spending a lot of time on both campuses, and look carefully into what you can pursue at each school (and others). Penn has a law school right on their main campus, and there is a great potential to do a work study job there. I was BME and did work study at the medical school; my brother did work study at the vet school. Don’t overlook the amazing resources and immediate area of the Penn campus.
IMHO, it certainly would be completely different at those two schools. 2,477 at Vassar undergrad and I don’t see that they have graduate school. 10,000 undergrad and 10,000 grad at Penn.