If you start at a large company with a reputation for only hiring top candidates, you will start your career with a higher salary, a great company on your resume, and experience in how world-class companies do things (both good and bad). These are your journeyman years, and will give you the experience, context, and contacts to be much more effective if and when you do decide to join a startup. It will also make you much more interesting and valuable to a startup (which will equal more equity).