My understanding was IUD was the best.
I was sold in 2005 - failure rate was LESS than sterilization.
I just did a quick web search and found a site which backs what my doctors told me. (They were really pushing IUDs - must save the HMOs $$$$ since so effective).
Contraceptive Info :: Birth Control Failure Rates
I guess a plus is that you don't have to remember to take a pill or get a shot.