The three main branches are Reform, Conservative and Orthodox. Orthodox is the most strict, while reform is the least strict, and the most liberal branch of the three. Conservative claims to be somewhere in between Orthodox and Reform, but from what I've seen growing up, I don't think there are any huge differences between Conservative and Reform, but this is just my opinion.
To narrow it down, you need to know exactly how observant you'd like to be; because the differences between Reform and Orthodox are practically night and day. Could you see yourself keeping the sabbath every week, and eat ONLY kosher food for the rest of your life? If yes, then Orthodox may be the right fit for you. There are MANY laws Orthodox Jews must keep, it really is a big, lifelong commitment. Or if you'd like to still be observant, just not to the level of orthodox, then Reform or Conservative may be a better fit for you. Oh, and one more thing: Reform conversions are not recognized by the state of Israel.
There is much more detailed information that goes with this answer, so perhaps you should read this before making your decision: http://judaism.about.com/od/denominationsofjudaism/p/branches.htm
Good luck with all of your future endeavors.