It's been a few years but I think this is all pretty current:
Aliso Viejo is close to Laguna Beach if you want to shore dive. Shaws Cove is probably the most famous (and crowded) SoCal dive site. Heisler Park is also popular. From the NW side of Aliso Viejo take Laguna Canyon Road to Laguna Beach. A right in town onto PCH/Hwy 1 and Heisler is a few blocks north. Shaws Cove a block or so past it. . Here's 2 dozen other nearby options...lol -
Directions to Laguna Beach California for Scuba Diving It's pretty cold so plan to rent/bring a 7Mil wetsuit.
Some shops in Laguna: Beach Cities Scuba has multiple shops in that area. I've been to their shop in Huntington Beach. Their shop in Laguna is called Laguna Sea Sports.
Beach Cities Scuba Centers ? Your premier Orange County Scuba Diving experience They also book Riviera - mentioned below and have a shop in Dana Point as well. There's also Southcoast Divers - IDK them.
The closest boat diving in that area is either from Dana Point - a little south down I5 or a longer drive north to San Pedro/Long Beach. You'll see Riviera mentioned here regularly - they're out of Dana Point. Or you've got all the boat options in both San Pedro or Long Beach - there must be a dozen of them or more. Here's the complete boat list:
California Dive Boats : The Official Page
The freeways in that area can be busy in the mornings, the 5 is a major route thru Irvine, Anaheim into downtown L.A. and the 405 is one of the Port of Long Beach access routes. A nice drive that takes longer is to drive into Laguna then up the PCH/Hwy. 1 through all the beach cities - it runs right along the water. Scattered along the road are some nice waterfront restaurants also. Parking in the beach cities is incredibly tight so if you see anything close, grab it.
Additionally you can catch the Catalina Express out of Long Beach, San Pedro or Dana Point and dive off Catalina for the day in the marine park - either off the shore or one of their local boats. Many of the Long Beach/Sand Pedro boats will go there also - I've heard some of them do better dives than what the Catalina boats do.
http://www.catalinaexpress.com/
San Diego seems like a stretch to me unless you want to day trip down there to dive the Kelp or LaJolla Cove. The better Kelp forest that's easily accessible in San Diego is off Point Loma via boat - they just about all go there. divebums.com lists most of your options in that area. To find parking at the Cove you'll need to be there really early. La Jolla Shores nearby is less crowded - and has a big parking lot - but IMO the dive isn't as good.
have a good trip.