your question confuses me....are you asking who "I" should marry? Or are you asking who people should marry in general...I know who I should marry, it's the girl in my profile picture. Now people in general should marry people who they get along with. People who they can solve problems with in a non stressful kind of way.
People need to marry people who come from the same mindset and for the most part, believe the same things.
Most of all though, people need to marry someone who they know they can truly spend the rest of their lives with, no matter what.