Probably sacrilegious to say here with as many WDW fans as there are, but I find Disneyland superior to WDW Magic Kingdom. Disneyland is great and I know you will have a wonderful time. WDW and the bubble as a whole are fantastic, but when comparing WDW Magic Kingdom to Disneyland I'm not much of a WDW Magic Kingdom fan and was actually a bit disappointed the first time I visited having been to Disneyland previously - it just didn't seem as immersive and magical as Disneyland always is.
I think 3 days between Disneyland and DCA is a really good fit. Both have plenty to offer and you should have no problem filling up those three days.
Not
DVC-related, but try to be in Cars Land at DCA a few minutes before sunset during your visit for the little lighting ceremony they do at sunset each day - it's not mind-blowing or anything like that but is fun and a fairly unique little experience. The evening shows at both parks are very worth-while as well.