Not everyone would agree that love marriages are better than arranged ones. In some cultures, it is believed that arranged marriages are more stable because the couple is picked for one another by people who are older and more experienced.
However, I would argue that love marriages are better because a marriage is, ultimately, about the relationship between the two people involved. It is not really possible for other people to know what kinds of people belong together. I do not believe that family members can do better than individuals themselves in picking a mate.
Of course, that is not to say that all love marriages work. However, I think that love marriages are better because they allow people the freedom to pick the mate that they want instead of having to simply accept the mate picked for them by someone else. In a relationship as intimate as marriage, that is vital.