What do you mean when you say "potency"? Are you asking which one causes the most growth, the most strength gains, or results in the greatest improvement in muscle quality? In other words, "potent" in what regard?
In terms of muscle-building, Dimethazine, a DHT derivative, is the best muscle AND strength builder for the largest number of people. 50 mg per day of this stuff will result in greater growth than an equivalent dose of D-bol or Anadrol. This has been proven by 1,000's of real-world experiences and even legitimate clinical studies conducted by Big Pharma (Dimethazine was a script drug in Italy and Mexico decades ago), in whicn Dimethazine was compared directly against Anadrol, testosterone prop, methylest, and Wintsrol for myotropic potency (muscle building power). Per mg, Dimethazine trumped them all by a significant margin! The stuff also makes you much harder and drier than Anadrol.
Many people also experience greater strength gains than they do with Anadrol and certainly D-bol.
It's hard to say what the next best mass & strength builder is, as there is no overwhelmingly clear winner..and not everyone responds the same. 1-Alpha at 60-80 mg daily is pretty damn strong, as is methylstenbolone at 40 mg daily. The 1-Alpha can be dosed higher than the M-sten due to a lower level of toxicity, but lethargy can be an issue for some with this drug.
Epistane is a good lean-mass builder when used at moderate-high dosages, but is not on par with muscle builders like Dimethazine. Still, 60-80 mg daily consistently produces significant gains in dry, lean mass.
SD, although now a controlled substance, was the best of the bunch. My favorite oral steroid of all time--by a LONG shot. Actually, it is my favorite steroid, period. No other drug has ever provided the same combination of massive size & strength in such a short period of time, along with an increase in muscle hardness and killer vascularity. It really does provide the best of both worlds. Some guys experienc lethargy--others don't.
M1T, now a controlled substance as well, was exceedingly potent when it came to raw mass gains. Just 30 mg of this stuff daily would blow anyone up in record time. It puts Anadrol to shame--it really does. I have seen some guys try 40 mg daily with crazy gains in size, assuming they are still able to eat. Along with its superior potency, it also has the worst sides of any steroid yet released (generally speaking). It pretty much screws up every health marker--hard on the liver, destroys lipids, massive BP increases, extreme lethargy, appetite suppression, etc, etc, etc, etc.
As far as which steroids you should stay away from, I can't possibly answer that question for you. Remember, these are just steroids--not rat poison. Even the worst of them (M1T) can be used safely, so long as dose and duration of use are appropriate. The drugs you should use are those that best meet your needs, whatever they happen to be...and when I say "needs", I am not just referring to one's muscle or strength goals, but to their overall circumstances--including health. Obviously, someone who already has high BP and a stressed liver is not going to want to add some M1T into his program. No matter what the drug is, its use should make sense for the individual.