The following is conventional wisdom... YMMV.
MM is Sun, Tue, Thurs, Sat. And DLR draws 70% day trip visitors which tend towards weekends.
In high season it is best to avoid weekends. In off-season weekdays have reduced entertainment and it is often better to overlap a multi-day trip over a weekend. See "What You Should Know About Off-Season at DLR"
www.disboards.com/showthread.php?p=18462889
The following discussion holds year round with the caveat that offseason weekdays have more downsides than high season weekdays as discussed above:
Best day to go to the DL park is Wednesday. No MM and furthest from weekends.
Next best is Tuesday/Thursday. These both have MM so are good days to use MM.
Monday is next best. And no MM.
Friday is next best. No MM. Fridays tend to be less busy in the day but get lots of local AP holders who stop in for the evening and so evenings crowds can be pretty bad.
Sundays are now considered to be worst. Saturdays not as bad as Sundays. This is a trend since MM was changed to be both Saturdays and Sundays.
As far as DCA, the same days pretty much hold. The difference is that if you are at DLR for several days it is best to plan a day to start at DCA when DL is having its MM.
If I had a three-day high season trip with one MM here is what I would do:
1. Go Tuesday-Thursday
2. Tuesday - go to DL and use MM. Hop to DCA mid-day if interested.
3. Wednesday - start day at DL at opening. Hop to DCA mid-day if interested.
4. Hit DCA at opening - if enough energy visit DL before DCA to collect some FPs and hit rides of interest. Return to DL late afternoon/early evening.
