This really depends on what your goals are at this point in life.

If you are looking for a fun city in your 20s where it is easy to meet people, I would strongly recommend San Diego instead. People all over the country move there for a few years in their 20s just to have fun, then end up moving away because it's too expensive for the jobs you find there. But if your goal is to really build your career and San Diego doesn't offer that, then that's not the best choice.

San Jose is simply not a very fun place for people in their 20s IF there's no connection to the area. It's expensive and outside of a nice variety of multicultural food and decent weather, there's not much it has to offer than any other city in America for the price. However, if it is the place to build your career, then it isn't a bad choice.

And heck, if we're just talking about the ratio of social/nightlife to cost of living, I would even choose Sacramento over San Jose. People in the bay love to look down on Sac but it makes more sense if you're a young person and the bay area is too expensibe for you. It's also much closer to Tahoe, which people in the Bay love to go to anyway.