C.A.
This park is really part of the whole 'Disneyland experience' now. If your kids like the movie Toy Story or Cars or even The Little Mermaid, this is the park to visit.
Also, if the adults in the group would like a glass of wine, alcohol is only served at this park and in Downtown Disney.
There is also a very large 'playground' in the California park that my kids always love to climb and play in.
The shows in this park are well done too.
I always like to get a park hopper ticket so my family can move between the parks with ease. Disneyland is considered a pedestrian park and walking is easy between areas.
You don't know how busy the parks will be. Choosing to have California Adventure available to you, may save your experience. There tends to be a ebb and flow to the crowds and if you are smart, I would visit the areas that are not attracting the masses. You can always go by at a different part of the day and see if they are less crowded.
Use the Fast Pass system to your advantage. If a ride is too busy in one park and you have accomplished everything else you would like to do, go to the other park and then enter again when the Fast Pass tells you its your turn.
Have a great time. Your children will love their time there. I don't think they will feel that California Adventure is a let down. It has the feel of Disney and at the same time is very different. (And this is very good if you have been one of those parents who have been on It's A Small World a gazillion times) Good luck!