Hmmm... that's a hard one! My instinct is actually to suggest California Adventure because of your familiarity with WDW and presumably Magic Kingdom. Disneyland IS beautiful, but compared to WDW, I'm afraid it's going to appear crowded and hectic to you.
California Adventure was built more recently and has the benefit of wide walkways that feel very open compared to DL. It is also unique in its theming, and while some of the rides are repeated in other parks, the concept of basing a theme park off of a place is interesting and original. (Admittedly the original concept was not attractive and this 'classic' redesign that came around the Carsland expansion is much more appealing!)
There are a few very cool and picturesque locations such as the awesome immersive Carsland, the Paradise Pier area, and Bugs Land. Grizzly River Run is fun, with a good amount of theming in the area, too!
DCA is a little weak on entertainment currently, but there are a few street shows every hour at the 'hub' near the fountain and Carthay Circle.
I love California Screamin and Radiator Springs Racers! Toy Story Midway Mania is super fun, but you have to hit it first thing or wait for 30-40 minutes. The line moves fast though...
I think it is totally possible to plan a great full day at DCA, but if you wanted to squeeze a few more operating hours in, you can consider the Park Hopper add on when you arrive and have access to both parks all day.
Have fun planning!