Multiple sets that follow a proven training schedule.
"Massive strength gains" are what every professional athlete and training team are looking for. The bros on bodybuilding.com and lurking in gyms across the world constantly think that they have unearthed the secret sauce to sick gainz, forgetting that there really are professional athletic organizations that make a science out of strength.
It's a long topic, but strength gains basically consists of constantly overloading yourself, balancing on the knife edge of too little (not enough adaptation) and too much (exhaustion / over training / injuries).
If you want to to bench 315 or squat 500, the training programs that they follow are very clear cut. There are differences, but they have a lot in common with each other. It's really shocking how very few people in gyms know anything about training.
Check out Westside Barbell's Program, the Texas method, or Madcow 5x5 if you're an intermediate lifter. Starting Strength or Stronglifts 5x5 if you're not hitting intermediate strength standards yet.
Honestly, if pyramid's/supersets/down-the-rack's or whatever else was a critical link in the chain to the Olympics or international records, you'd see those athletes making it a core component of their training. They simply don't have the time of flexibility to add non-essential "stuff" into their training.
Body builders, dudes on juice, and your general gym rat are a whole different ball of wax, but that's not the pursuit of pure un-adulterated strength.