That depends on a lot of things:

Where do you want to fly to/from? You're in California: within the U.S., to Asia, elsewhere?

How do you want to accumulate miles toward those award flights? From other flying? In that case, which airlines serve the routes you'll fly on, and in which class do you expect to fly?

Do you hope to earn a significant number of miles from credit card spending, hotel stays, and other non-flight activity? In that case, what kind, and what can you tell us about your spending/usage patterns in those areas?

Bottom line is that this simple question has no simple answer. If there was a simple answer, everyone would join that program and fly that airline. Other airlines would see this and modify their programs to compete. As soon as that happened, the answer wouldn't be simple any more.

(BTW, in some cases the answer is "no program at all." Some people are better served by using a cash-back card and buying tickets with the money they save. It all depends.)