We've never had any real problems with US immigration, it's slow certainly but not as slow as Marrakesh going in and leaving, and the TSA will open your bags, even cutting off TSA locks. The arrival document that you're given on the plane is a nuisance, what's the point of the ESTA? The people working on immigration can be abrupt and humourless, but can also be pleasant and chatty but as everyone's said don't try and make "funny" and "ironic" remarks, the Americans don't do irony!
Enjoy you trip, hope Disney lives up to your expectations