Air Down+Circle from any single jump height can confirm into level 2. It works both in combos and by itself. For most characters you activate the super at the peak of the juggle for it to connect; for smaller characters you have to let them drop a bit before activation.
The only reliable way to combo into level 1 is with empty cancels. The other ways are either too situational and may not even be true HC's. I've never been able to register j.Forward+Square (both versions) or Forward+Square as a HC in practice. Maybe it's just me though.