Hardest Routine

What’s the hardest weight training routine you guys have ever used? Also, and more importantly, did it work? I would have to say the “C” leg workouts from Fred Hatfield’s “Hardcore Bodybuilding” book for me. And it worked very well in adding size, though I tweaked it a bit.

Would be the original GVT routine 10x10, and the first week of Ian Kings 12 weeks to super strength (what a shock), and both work well