I grew up near DL and went on day trips at all times of the year. Now I live out of state, and we go to DLR as a family once every couple years. We sometimes sneak in a day trip in between.
I remember as a kid when we would go during off-season and being disheartened when we walked up to the gates and see the signs listing all of the rides that were down that day.
If you go to DLR more frequently (at least twice a year), then having rides down is not a very big deal. If you go less frequently (like we do), then it is a bigger deal. I concluded a number of years ago I would rather go to DLR when I could expect the maximum number of rides and shows to be available.
The above is the basis for "HydroGuy's High Season/Off Season Tradeoff Rule"
www.disboards.com/showthread.php?t=1199852
For apparent examples of this, see "Fantasmic removed from the Jan. calendar!"
www.disboards.com/showthread.php?t=1300293 and "POTC Ride Down For Refurb #2 - Possibly Feb-May 2007"
www.disboards.com/showthread.php?t=1222667
So in answer to your question, I prefer to go to DLR during high season. Yes, that means more crowds, but within high season there are less crowded times - for example, avoid high season weekends and holiday periods to avoid the worst of crowds. Plus, since we stay at a nearby hotel, we use that to our maximum advantage over the day trip visitors which make up 60-70% of visitors to DLR. This means to get to the parks early, take a break in the afternoon when the parks are most crowded, and then stay late each night.
In addition, I especially like DLR when the weather is warm. Heading out at 7-8AM in shorts and tee-shirts, and then hanging out at DLR until midnight, still in light clothes, is just so comfortable. Finally, during high season the park hours are at their maximum - DL is typically open for 16 hours per day, and DCA for 12 hours.
Put all of that together, and summer weekdays are my favorite time to be at DLR.