Well, just did HCE # 2 this morning and my legs are still quivering! That's tough - like the other poster said - especially during the blasts.
HCE # 3 is a good one, as is HCE #1.
MIC is a killer, but after IMax 3 and the HCE series, I don't find it as tough as I did before.
Circuit Max always kicks my butt (especially when I skip the Upperbody part and do only the lower body with heavy weights - I'm tripping over my step by the time the last step routine is done).
Leaner Legs and GS Legs always get me.