Choosing your advisor is like choosing your spouse.I would say more like choosing your parent since the advisor-student relationship is not symmetrical. But the point remains: No single decision will make or break your graduate career more than the choice of advisor.
A good advisor serves as a mentor and a colleague. Someone who will represent you, fight for you, challenge you and push you but not belittle you or take advantage of you. He or she will direct your research to primarily address your future career. An ideal advisor-student relationship will develop into a mutually strong research environment and will last well beyond the student's graduate career.
You should ideally choose an advisor whose expertise matches your research interests. But more importantly you need to find the advisor with which you can have a strong working relationship. You don't have to see eye-to-eye on every issue but you need to have mutual respect. Like in marriage, an advisor might work well with one kind of student but not with another. You need to find the right advisor that fits your needs and personality. If the advisor relationship goes sour for any reason, you need to change advisors. Being stuck in bad advisor-student relationship is almost a guarantee of a disastrous graduate career.