Love is clearly the most important. The other three are of equal value to each other.
Without Love the relationship is doom to fail. It doesn't need to be the traditional American view of love, but any form of it is acceptable. Without love there is nothing. You don't need the others if you don't have love.
Sex is nice and can help strengthen love in a relationship, but it is not completely important. Many relationships have done well without it. In fact, my relationship is one of those.
Communication is important because without it there is an increase in the chance of having fights and that can either hurt the love in the relationship or make it stronger.
Honesty is important, but not so much as communication. It depends on what kind of honesty you are speaking about. It's okay to keep things from your partner as long as you know it will not hurt the relationship or put your partner in any kind of trouble.
I hope that helps out.