We' ve been to WDW in September, October, November, January, February and May and, by far, the parks were the least crowded in January. That said, however, we've decided on October for our upcoming trip because the weather this past January was a little too cold for us. We were only able to go to Typhoon Lagoon 1x -- just barely. If you're willing to forego the water parks and/or swimming at your resort/hotel, then it is a great time to go. If swimming and/or water parks are really important, you may want to try another month.
We've always made our reservations through Priceline so I'm not able to help you out with value season vs. regular season. If you're willing to try Priceline, you can get some amazing deals no matter what the time of year.
Good luck planning your trip.