The first amendment is the first answer, and though the second 1 is opinionated my top three are:
1st Amendment (Freedom of Speech) because it allows the nation's people to openly speak against or for whatever they want with little to no restrictions
5th Amendment (Right to a Jury and right to remain silent) because it allows you to have a fair chance to prove your innocence in court and you will not self-incriminate without being told your right to not do so
2nd Amendment (Right to Bear Arms) because if you are going to protect yourself and your family, why not do it with one of the most powerful weapons mankind has ever created?