THAT is the question of the day. If you can go in the spring and time it with the Cherry Blossoms blooming, take D.C.
It won't be too humid or hot yet and your walking around will be more pleasant than summer or winter. The nights will be brisk but not cold and the colors, man let me tell you, the colors are magnificent. Truly a site to behold.
There is so much to do there both mainstream and off the beaten path. There are enough people here with info to put you in some great restaurants and places to see.
People travel for different reasons. When Im looking to relax, drink way too much and not think for 5 days, all inclusives can be nice. When I am looking for adventure....not so much.
I think the same can be said for your situation. Are you looking to learn about DC and all that goes on there or are you looking to relax? I hear that you will do a lot of walking in DC so if you want to just hang out and do a few excusions over the week, I would take the cruise.
I have been on 5 cruises, and been to DC 3 times on vacations. I don't know if you have kids, or your purpose of travel. I agree with the above poster about all inclusives being great to relax and to be a no brainer... and to eat and drink a lot. There is litte adventure, save maybe some of the excursions.
DC is ok, but I have been there and done that enough. I have been to the recently redone American History Smithsonian, and it looks truly terrible. It actually pissed me off. There is a great deal of walking in DC, and we had or small daughter with us, and that was a pain at times.
Both are great trips to me, depending on what you want to do.
Ha! When I lived there I felt the same way. I had to carefully plan my trips to certain places to avoid tourists. I NEVER hit up the Smithsonian Museums on weekends. They were avoided like the plague.