I don't know much about what it's like to do a PhD in physics at Berkeley, but many years ago I did a PhD in physics at Stanford starting out working in experimental quantum optics. I wound up doing something completely different, and felt supported in changing what I worked on. Stanford felt small in a good way, the grad student admin staff was wonderful. Stanford definitely has a different more suburban isolated vibe. Summers felt like you worked at a country club or something.
Who you work with really matters (obviously) and different PIs and labs can have very different cultures which you may or may not feel comfortable with. That alone can make your decision if you are very sure about what you want to do and who you want to work with.
Outside of that, I would say Stanford is a really great place to do graduate work, especially if you're not entirely sure what you want to do.
All of this is with the obvious caveat that my experience is from quite some time ago.
Who you work with really matters (obviously) and different PIs and labs can have very different cultures which you may or may not feel comfortable with. That alone can make your decision if you are very sure about what you want to do and who you want to work with.
Outside of that, I would say Stanford is a really great place to do graduate work, especially if you're not entirely sure what you want to do.
All of this is with the obvious caveat that my experience is from quite some time ago.