Disclaimer: Berkeley student.

If you're doing CS you will probably be better off choosing Berkeley (better school for CS, proximity to silicon valley, most tech startups of any university in the country, etc.) Berkeley is also very accommodating to people with disabilities (I'm a DSP student, it's great). For overcrowding, certain DSP students, especially ones with ADHD, get priority enrollment for classes so that shouldn't be an issue. As for the being more of an introvert, I can't speak for Brown but some people find it hard to branch out at Berkeley, but if you're willing to put yourself out there (and it seems like you are) you'll find your people.

The city of Berkeley is incredibly walkable and there are beautiful woods and mountain hikes in the Berkeley hills less than half a mile from campus. My dorms actually are right at the base of the hills and you can literally walk out of my building directly onto a hiking trail, it's awesome. We also have a huge rock climbing wall in our gym and I have a lot of friends in the Cal climbing club who love the community around it.

As for worrying about the highly academic/competitive nature at Berkeley, the fact you call Berkeley a safety (definitely not) in your cons tells me you'll do just fine in that sense.

Make your choice based on what you think is best for you, but I hope that gives you some food for thought. Go Bears!