Hi Bec. Welcome. I've been to the caribbean several times. In February, we cruised out of Long Beach, California, down the Baja Coast to the Mexican Riviera. It was breathtaking.
I'm partial to the caribbean for it's crystal clear blue waters. You can't compare the snorkeling/diving. It's much better in the caribbean.
On the flip side, seeing whales breaching, sea lions basking on rocks and dolphins/mantarays following the ship are indescribable, to say the least. The rock formations that jet out into the sea are glorious. The coastline is beautiful. Cabo San Lucas and Mazatlan were both great ports with friendly, helpful locals.
We spent 4 days in L.A. sightseeing and that alone was fantastic. We did Disneyland, Malibu, Santa Monica Pier, Hollyweird, LaBrea Tar Pits, plus much more. It was my first time on the West Coast and I thoroughly enjoyed it.
It all comes down to what YOUR interests are and what you hope to get out of your cruise.