Once you limit it to when the kids are not in school, you just put yourself in the "crowded" category.
We are teachers and also limited in times we can go. For this reason our favorite time is July. Yes, it is crowded, but we figure the summer season is longer than Easter or Christmas break and can spread the crowds out over the summer months. Also, traditonally, if you get there at opening you can get a lot done before the crowds come. I say traditionally because of the new DCA opening and I don't know how it will affect the crowds this summer.
July can be warm or even hot but never humid so I don't mind the heat so much. I also like July because it opens early, stays open late, and the SOCAL APs are blocked for the summer. And all the attractions are up and running. I've always wanted to try going right after Christmas and New Years break and I imagine the crowds are light, but then some of the attractions are closed to take out Christmas decorations or for refurbishment.
And then there are the people say there is no more "off season" at DLR. To me, more importantly than when to go is just pick a time and get there at opening and use FPs.
Oh, be sure to see this post by Hydroguy:
http://www.disboards.com/showthread.php?t=1162599 DLR for WDW vets.