You obviously have a misconception about how PHs work. And it also seems like your diet is poor by the fact that you said you've tried multiple PHs with not much success. The biggest factor in your gains is diet, no matter whether you're doing it natural or on anabolics. There is a possibility that you could have been unlucky and bought bunk products, but i kinda doubt it.
You want gains that don't taper off? Sorry but that's what happens when you cycle off. With oral steroids there will be a decent to substantial loss of strength and weight post cycle. That's just how orals work. Gains come easy on cycle, and if you don't have a great diet to begin with, you'll lose most if not all of what you gained after you cycle off. If you do have a solid diet, you'll keep most of the progress you've made.
Certain PHs are great to start out on. They will be a good chance to see whether your diet is in check, or if it isn't. If you can run something like P-Mag or H-Drol and make good gains and keep them, then you're ready for something stronger. If you can't keep most of your gains, then you're not ready. There's no point in taking SD or dymethazine and extremely taxing your liver just to simply flop on your cycle.