I think the DTD security checkpoint is almost always quicker than Harbor.
The walk to and from the park would albe more peaceful. The
Disneyland Drive walk is the same distance from S Harbor/Katella but there aren’t any businesses on that block so there’s usually less pedestrian traffic and almost everyone is going to and from the park. S Harbor is a very busy street with lots of vehicular and pedestrian traffic. There are lots of stores that attract a decent amount of transients. Usually it’s not a problem but for me personally it’s not something I feel like dealing with on vacation with my kids in tow. My opinion. Hope that helps.