For crowds, I'd avoid any time schools are typically on breaks for the holidays and even for summer. Spring break and the weeks of Christmas and New Years can be some of the highest crowd levels at the parks. I would recommend January (avoiding MLK Day), February (avoiding Presidents' Day), early May (after Spring Break crowds and before Memorial Day/Summer crowds), September (be prepared for rain, always get travel insurance, but fall decorations are up!), early November (before Thanksgiving week, fall decorations are still present), and early December (Christmas decorations go up by the first weekend in December usually, before the holidays).  For weather, if you're vacationing to Walt Disney World, you'll likely have an afternoon shower nearly every day.  It's central Florida and there's no getting around that.  Just pack a poncho and enjoy the lighter crowds in the afternoon when people head back to their hotel!  Hurricane season is June 1 to November 30 with the peak times being mid-August to late October so that is definitely something to consider, especially if sailing with Disney Cruise Line in the Caribbean or Bahamas. Protect your vacation during these times always with Travel Insurance.  For cruises, I recommend January and February (a great escape from Winter!) and November and December. As far as Disneyland, every day is beautiful in southern California!