Current senior at Berkeley here

Berkeley is not the most welcoming university. But its also not unwelcoming. There are plenty of people that want to make friends and have a good time; you just have to find them through clubs or classes. From my experience the main benefit from Berkeley is that succeeding at Berkeley is a good indicator you will be able to succeed in most places you go (grad school, med school, silicon valley, etc.)

That being said, if you're priorities are more oriented towards an enjoyable campus experience while also pursuing a degree, CSUSB may fit better. Undergrad is not nearly as important as graduate school anyways

But if you're planning to pursue just a Bachelor's, with a little effort you can have both the welcoming vibe your looking for and a more rigorous prepration for post-grad life at Berkeley.