Laguna Beach will be more restrictive on size and height. Several considerations come into this:
hillsides can slide, neighbors views are prized, and the coastal commission doesn't want change. Laguna Beach planning process is slower than Laguna Niguel.
Laguna Niguel is built with more Home Owner Associations, therefore you will have Laguna Niguel city planning requirements but also the HOA will have some say as to size, architectural style and even paint color.
In both cases I would suggest you hire local architect and local engineering as they can tell you what will or won't get approved.
There are more construction projects underway in Laguna Beach that Laguna Niguel. This is because of a couple factors: Laguna Beach is much older community. Houses vary in style and age. Laguna land is more costly because the community is prized and the ocean or canyon views.
Laguna Niguel was a master planned community becoming incorporated in 1989. Laguna Niguel that is closer to Dana Point and Monarch Beach has ocean views.