As I do have an AP to disneyland. There really isn't a good day. It'll almost always be packed. If possible, plan ahead and utilize the FAST PASS where available.
Don't quote me on this. but I think 4/3 would be ok for disneyland, maybe. That's when the iPad comes out and with the current rumors that it may be hotter than the iPhone. Mostly everyone may all be at an apple store. And as said earlier, 4/2 & 4/3 all AP's except the Premium are blocked out.