DCA for sure!! metro is so easy to get around. You can get transport passes if they suit your needs. Dupont Circle area. If it's budget, you can stay Comfort Inn Pentagon (discount for DL) and ride metro

or if you have kids and want to splurge with some good perks: 2 adults/2kids:
Savoy Suites Hotel in Washington, District Of Columbia - Hotel Vacations | Family Getaway
new customers can get discount code for $ off. It nets out $900 tax incld for 4 with 1 day DC Power Passes and BFasts--all atop Georgetown (oooh spoooky, you can see the exorcist house and steps!!) It also has a Nightitme tour that sounds pretty interesting included