Trying to decide on week for 1st trip to DL; due to school & works schedules; we usually travel either:
3rd or 4th week in June
week after Columbus Day or
1st week in December
DH wants end of June to extend the trip to visit Vegas too; i'm thinking DL for 3 or 4 days; Universal a day, a cititour and Knotts would certainly amount to a great vacation and no need to rent a car either for long drive to Nevada.
What do the experts say?
Well I am biased towards the fourth week of June because that is when we are going.!

This year the problem with the third week of June is that it is soon after the Finding Nemo sub ride opens which is going to impact crowds. I do not know for sure that the fourth week will be better than the third week, but I believe it will be this year.
Personally I like summer visits to DLR, but am probably in the minority around here.
As you are new to DLR it is important you understand scheduling differences from WDW. WDW runs show schedules (fireworks, parades, etc.) year round, with higher frequency during peak times. So you can plan a trip for off season and still be in position to experience the entertainment year round. Not so at DLR.
At DLR they run a full show schedule during busy times like Spring Break, summer, holidays, but otherwise many of the shows are only offered on weekends. At DLR weekends are pretty much like high season year round because there are tons of locals who visit DLR primarily on weekends. So the crowd differences between weekdays and weekends at DLR is much more significant than at WDW. So if you go on "offseason" weekends to be able to see the shows, then you are really doing something comparable to high season.
If you go in October then that may be the least crowded of all the weeks you listed, but also the most likely to have rides down for refurb and limited show schedules (see "HydroGuy's High Season/Off Season Tradeoff Rule"
www.disboards.com/showthread.php?t=1199852)
December will be high season, and if you go during that time then the first week of December is a good time to go (compared to other holiday period weeks). You will have Christmas decorations, but also be at most risk for colder weather.
If you think more seriously about a summer visit, then here is some info that will help you: "Getting The Most Out of a Summer Visit To DLR"
www.disboards.com/showthread.php?t=1345319
And a lot of people have benefited from my lengthy "A DLR Guide for WDW Vets"
www.disboards.com/showthread.php?t=1162599