We have been to Disneyland and DCA many times. A day in the middle of the week is always a better choice (Tuesday, Wednesday or Thursday). If you are interested in fireworks shows you'll have to check the web-site for the schedule.
I am on the fence on which park is better. I agree that the "Disney Magic" feel is better at Disneyland. Space Mountain, Indiana Jones, Big Thunder Mountain (newly refurbished) and Splash Mountain are great for the big kids. (We enjoy some of the little kid rides too, Buzz Lightyear and Pirates of the Caribbean are fun.)
DCA has Radiator Springs Racers which is a fun and thrilling ride (get there early and get a fast pass or you'll be in line forever!!) Tower of Terror and a rock and roll indoor roller coaster. There is also a fun water ride (watch out you'll get wet, but it's lots of fun). Unfortunately Soarin' over California is down and being refurbished right now.
If it were us we'd do two days, one for each park.
Have Fun!!
M