Visit both parks - you can go shopping anytime.
Does this mean you have only 2 days? If so I'd spend 1.5 days in DL and 1 in DCA.
Others have their favourites, but if I were to return I'd definitely do again:
Splash Mountain
Haunted Mansion
Pirates of the Carribean
Peter Pan
Indiana Jones
Winne The Pooh
Big Thunder Mountain rail road
Small World (yes, seriously - it's very good!)
Star Tours, Honey I Shrunk the Kids, Jungle Cruise were also cool.
In DCA I'd do:
Soarin over California
Grizzly River Run
Tower Of Terror
Screamin is good if you like coasters.
I'd also make sure I saw the fireworks at least once, and the parade.