Commitment

Generally men. They are predisposed to mate with as many females as possible whereas the female is predisposed to seek security so she may have safety for the children she bears.

As for the modern world when all things are equal I would say whomever has bad experiences and has the most to lose or gain. Those who have had higher quality relationships are less likely to simply dive into a relationship until secure that the new prospect is at least equal to the old whom they left and, if they risk the safety of children or personal resources it makes them more gun shy.

So, the answer would have to be 'depends.' If a girl's crack head abusive boyfriend gets thrown in jail, I imagine she might pick up with anything however, if a rich widow who lived a fairy tale romance with her departed husband of thirty years contacts you or is contacted, it is doubtful she will simply throw it all in with the first guy who comes along.

I know this helped like a hole in the head but all things are not equal when posing a question such as what you presented.

Probably men, for the reason given in the 2nd comment. Women though, independent ones might also be afraid of committment, esp. if they've had bad experiences with their ex-husbands or ex-boyfriends. Whom to trust - might be the next question, that would be hard to answer.

I think they both are equally afraid. Every once in a while someone comes around that makes a person feel like that they would give anything just to have that particular person, and commitment, seems like no big deal, an easy thing to do.
But then they worry about what is it the other person feels, and are they on the same page. And even though they really would like to open up, they do not for fear the relationship is one sided.