Peace
Almost everyone lacks something in their life. It seems that Hashem holds back one thing to keep that person praying.
Many cannot find a decent job to comfortably support their family. They pray over and over again for a livelihood. So many times a day! This is their prime concern in life.
Then there are many who have enough money, but cannot find a good Wife. This is their prayer over and over again, "Please G-d, send me a good wife today. It is not good to be alone." Thousands of times over and over again they beg Hashem to solve this problem for them.
Then there are Jews who have a decent livelihood, a good wife, but they have no children. They pray oh so many times a day for Hashem to give them healthy, happy, children. Children become the most important blessing in the entire world for them. They feel totally empty because they have not received this blessing.
Then there are those who have a livelihood, a good wife, lots of great kids but they are not well. Their sickness is clearly the most important thing in the world. "Hashem, please heal me."
When you are at peace you are satisfied. Your prayers are mostly prayers of thanksgiving or for others who are less fortunate than you. If a person has peace he or she has all their problems solved, or feels that they are on the way to being solved. In any event these blessed people are satisfied with their lot. It's no wonder that Hashem chose Peace to be one of His Names…Shalom.