I personally (and I'm not sure, but I'm guessing Hydroguy would agree with me) would rather tour the parks when it's more crowded than not. He has a thread about it, but basically I'd rather go during busier seasons than off seasons because:
-Full entertainment every day/night (nightly fireworks, fantasmic, electric parade)
-Longer park hours (I love getting to the park at 8 and staying until 11 or so)
-Pretty much all rides open (unless there is a very lengthy refurb happening, otherwise, the least crowded times of the year are when the rides go down for refurbishment)
Crowds aren't really a big issue if you have a good morning plan, use FP, and be flexible.