I disagree with many of the posters here. You can’t really experience the benefits of a small LAC through cross registration. If you choose Penn over Williams, you’re giving up on a LAC experience. Taking classes at Haverford or Swarthmore is not the same as being a student at a small LAC. Like at Penn, much of your learning will be outside of the classroom. It matters if that classroom is a university of tens of thousands in the middle of Philadelphia, or if it’s a small college of two thousand in the Berkshires. When I had to decide on colleges, one of the reasons I ruled out Williams was because it was too isolating to be in the mountains. And one of the reasons I ruled out Penn was that it was too chaotic to be in the city. And this is coming from a city girl.
Nonetheless, I did and still do see the benefits of a small LAC and I absolutely do not believe that any college will be like the “real world.” For four years of your life, you can choose to spend it learning the way you want to. And afterwards, Williams will not hurt you if you want research experiences, recruiting, or real world experiences. Especially for Physics, since that is one of their strong suits. It has always been, and will likely remain, a place that produces outstanding graduates.