You have a huge selection of cruises to choose from, and I suggest that you do your research and then see a TA. Also, there are some excellent cruises that go round trip from Los Angeles and San Diego. And if I were a first timer I would look at RCCL and Princess, as there cruise lines are the all purpose cruise lines. This means that they have something for everyone at a reasonable price. Celebrity is for persons who enjoy a ship with a European ambiance and HAL is really for older affluent, retired persons. Both Celebrity and HAl are outstanding cruise lines. Carnival is for younger cruisers who could care less about food and service.
The above is based on my 17 cruises and an 18th to alaska coming up in three weeks.
Hope that this helps.