"best" resorts is a subjective idea. Are you looking for least expensive, or nicest theme or convenient location?
Basically, you'll have to get a feel for it. For our family, the resort is just a place to sleep, so we prefer to spend less and we stay in a value resort. For those who want to spend more time in the resort and atmosphere matters more, they may feel the extra money spent on a moderate is worth it.
As far as discounts, you can book now and then watch for discounts to come up that may apply to your stay. If you Google search for Disney World Historic Discounts you might get an idea of what to expect, but it is most definitely NOT a sure thing until they are actually released.
