It's one factor of many. In my (limited) experience:
1. Initial interest in a partner is almost entirely aesthetics and charisma.
2. Girls are also often attracted to dominance, so charisma often comes before looks. Making people laugh can be a manifestation of this, but it's really about confidence*.
3. As you get to know them, it becomes more about personality. Many people will have experienced the phenomenon where, as you become attracted to someone, they actually seem to look better / you become more attracted aesthetically too.
4. I would say the ability to make you laugh (as opposed to other people) comes quite late on. It's more of a 'friendship' quality - something you look for in a lifelong partner. This may be personal preference.
*It's also been shown that how other people perceive your potential partner has a massive effect on how you perceive them. There was some kind of study where the same guy was shown to two groups of girls (individually). With one group he had a friend compliment him during the introduction, and with the other he had a friend ignore him / act cold. You can probably guess the results. I can't find the link though.