There are not too many seasons anymore where WDW is really uncrowded - if one exists, Disney will throw in some incentive to people (free dining, State discounts, whatever) to fill up the parks.
That being said - I think I’d prefer April (but not around Easter) over March Springbreak. Springbreak is just scary!:eek: The weather will be nicer in April too. Actually my dd and I took an impromtu trip the first week of March, a couple of years back. It was an excellent time to go - really quiet - but rather cool.