I use Neutral Special (3), Up Special (1), Down Special (1), and Side Special (2).
NS (3) has better range than I anticipated, and far better KB, as well. I killed with it around 150%. It self-charges, and can be used to limit options while your opponent is off the edge. If laser canceling was still in, I'd probably go with NS (2), but since it's not, I'm going with this one.
I stuck with the standard Up Special, because it seemingly goes the farthest, and I feel the safest while I'm doing it. There are multiple hitboxes at the beginning of the move, and an extended hitbox throughout the rest of it.
The standard Down Special stalls in the air AND has a hitbox. The other two don't have hitboxes, and DS(3) doesn't stall (DS2 might not stall as well...I can't remember). DS (2) has a wind box, but it doesn't push back significantly enough to compel me to use it.
I use Side Special (2) because the ending frames create an AoE explosion, that does decent KB. There are no hitboxes until the very end of the move, but Fox travels just as fast as he would with SS(1). The explosion of SS(2) is slightly delayed, which might cause someone to think you're vulnerable for an attack. But then the hitbox comes out and they get hit before punishing the lag of Illusion. It's not guaranteed, but it's a possibility, and I like it.